trivial: Fix compiler warnings

- Mark unused variables unused
- Initialize uninitialized variables

pc99, ltimer: Downgrade expected errors to warning

- If the ACPI isn't present don't try and parse HPET info.
- Don't print an error in function used to check if acpi tables are
accessible.

pc99,ltimer: Don't program timer if timeout small

If the timeout is smaller than the minimum timeout then don't try to
reprogram the timer.

pc99: Ack interrupts before handling timer

PC99 interrupts are edge triggered and not level triggered so interrupts
should be acknowledged before handling any hardware related operations.
This commit changes the PC99 ltimer so that a custom IRQ callback is
called instead of the common callback. The custom IRQ callback
acknowledges the interrupts before handling hardware operations.

libplatsupport: Refactor the internal handle_irq

Now that the handle_irq functions are no longer externally visible, this
commits refactors the handle_irq functions so that they can be accessed
internally. Also add logic to invoke the user supplied callbacks after
handling the timer IRQ.

libplatsupport: Remove handle_irq from ltimers

The 'handle_irq' function is no longer necessary and shouldn't be called
externally as the IRQs will be managed by the IRQ handling functions of
the IRQ interface.

libplatsupport: Allow user callbacks for ltimer

With the IRQ changes to the ltimer, IRQs are now managed internally.
This poses a problem with the management of the time manager and other
services which rely on having known that an interrupt arrived for the
timers. This also isn't a good idea as it presents a leaky abstraction
in that the services infers events based on interrupts received.

This commit adds the ability to allow users to supply a callback
that'll be called when certain events occur for the timer, e.g. timeouts
and etc.

libplatsupport: Add IRQ register logic to ltimers

This commit adds IRQ registration logic to the ltimer driver level.
Instead of treating interrupt allocation being a OS/environment specific
thing, this commit now uses the OS/environment agnostic IRQ interface to
register these interrupts. Also fix bugs/clean-up the logic of the init
and destroy functions.

libplatsupport: Try and handle ETIME errors from hpet

There is no way for the caller of this function (as it is part of an abstract interface)
to know how to resolve and recover from this error. As such this change attempts to
first recover from the error internally, and then panic if that fails.

libplatsupport: Refactor ltimer_describe_with_rsdp

Moved ltimer_default_describe_with_rsdp into pc99 timer
implementation.

libplatsupport: Modifications to RSDP parsing

Moved the parsing of the RSDP out of the table parsing procedure,
(_acpi_parse_tables). If the RSDP is not provided for ACPI
initialization, it will be searched for in the BIOS segment.
Modified the acpi_t struct to store the whole
RSDP object rather than the physical address of the object.

libplatsupport: Initialize ACPI with given RSDP

Enable ACPI initialization by passing an RSDP object rather
than searching for it within the BIOS section. Updated default
logical timer initialization to initialize the ACPI with a given
RSDP object.

platsupport: convert EINVAL to ETIME for pit

When we use the pit to set an absolute timeout it's possible the time is
too small, in which case the pit will return EINVAL and the absolute
time has already passed.

platsupport: set further irqs in pit ltimer

If a user requests a timeout that is too much for the PIT (> PIT_MAX_NS)
set the irq to come in at PIT_MAX_NS but also add another timeout in
handle_irq until the timeout requested is satisfied.

Periodic timeouts > PIT_MAX_NS are still not supported.

platsupport: expose pit constants, improve pit ltimer

- expose pit constants (min and max ns it can handle)
- modify pit ltimer to be able to set absolute and relative timeouts for
the pit that are greater than what the pit can handle by setting
a shorter timerout
- however, periodic timeouts which are greater than the max value the
pit can handle are NOT yet implemented
- otherwise just set a shorter timeout
- update pit error messages and codes. As the PIT is not an absolute
time source it doesn't make sense to return ETIME, instead return EINVAL
as the arguments are invalid

platsupport: request tsc freq from pit ltimer

libplatsupport: Explicitly disable PIT if it would collide with HPET

Given that the current timer interface assumes no multiplexing of timer interrupts this
change attempts to make sure the PIT is in a state where it's not generating interrupts
if the HPET is being initialized to use the shared HPET line.

libplatsupport: Declare 'error' variable at start of function

This is to prepare for adding new code before the original declaration of the
error variable

libplatsupport: Remove include for library we do not depend on

Platsupport does not (and is not suppose to) depend upon libsel4, which is where
this include file comes from. As a result this library will fail to compile if
the libsel4 headers don't just happen to be in an include path

This commit duplicates the desired constant from the header until a proper
refactor can be done

libplatsupport: Explain HPET delivery location

libplatsupport: Correct polarity of HPET interrupt

The HPET is defined in the specification to always be active HIGH, regardless of whether
it is configured to use level or edge triggered delivery

trivial: fix licenses

Add ltimer implementation for PC99

Users either the PIT + TSC or HPET