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.

platsupport: remove static init in ltimers

The regular init functions can be used with an implementation of
ps_io_ops_t that is a static implementation

platsupport/imx: Implemented ltimer_static_init

Created an ltimer static init function. This allows the user
to pass in pre-mapped vaddrs for the timestamp and timeout
timer devices.

libplatsupport: Refactor ltimer_describe_with_rsdp

Moved ltimer_default_describe_with_rsdp into pc99 timer
implementation.

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: Check function pointer is not NULL

platsupport: More accurately define ltimer_reset

Clarifies the documentation on ltimer_reset to indicate it should reset to an initial
state and that its affect on the monotonic counter is implementation defined, and not
strictly reset to 0 as previously claimed.

platsupport: clarify ltimer irq handling

trivial: fix whitespace

platsupport: add ltimer interface as logical timer

- add ltimer.h with ltimer interface (will replace timer_t)
- add irq.h with types for tracking irqs