Fix trivial comment typos.

Fix licenses (the rest)

SELFOUR-836: Hardware debug API functions should take tcb_t and not arch_tcb_t

Touches files all throughout x86 (32 and 64) and ARM.

s/D61/DATA61/ in license headers for consistency

ia32: Always use IRET instead of sysexit when single stepping

Previous code to return to user level performed
popf
sysexit
The popf was just before the sysexit as there is a one instruction
delay on the trap flag taking effect and ensured we did not attempt
to single step the kernel. Unfortunately there is not a one instruction
delay on enabling the interrupt flag, and as a result an interrupt
can be taken prior to executing the sysexit instruction. It is
possible to exploit this to escalate a user level thread such that
it is running with CPL0
This commit changes the restore paths to perform
sti
sysexit
Which will correctly delay interrupts until the completion of sysexit.
As the popf is now being done earlier to prevent single stepping the
kernel we return via an iret, instead of sysexit, for threads that
have single stepping enabled. To achieve this we
* When loading debug state if we enable the Trap flag we also manipulate
the register state such that the iret return path will be picked
* As fastpath_restore does not have an iret return path we forbid
the fastpath from switching to threads that have single stepping
enabled

Replace #pragma once with include guards

x86: Define FLAGS bits instead of having magic numbers

x86: Rename [ER]FLAGS to FLAGS

Having a different name for the FLAGS register creates an unnecessary difference
between ia32 and x86_64 code since regardless of the name/size the bits in the
register mean exactly the same thing

SELFOUR-499: X86, ARM: Add userspace invocations for hardware debugging

This commit implements the body of SELFOUR-499. The API exposes the x86 DR0-7
and ARM coprocessor 14 features to userspace by virtualizing them as context-
switched registers in the TCB. Implemented as TCB invocations. This feature is
only built when CONFIG_HARDWARE_DEBUG_API is selected.

* Add low-level support routines for setting, unsetting, getting, enabling
and disabling breakpoints.
* Add support for single-stepping as well.
^ Single-stepping is not supported on ARMv6 since the hardware
doesn't have support.
^ ARM implements single-stepping as instruction breakpoints
configured to fault on every instruction -- this is achieved through
the "mismatch" mode, which is only supported from ARMv7 onwards.
* Also support explicit software break requests, a la "BKPT" and "INT $3".

* New invocations:
* seL4_TCB_SetBreakpoint().
* seL4_TCB_GetBreakpoint().
* seL4_TCB_UnsetBreakpoint().
* seL4_TCB_ConfigureSingleStepping().
* New constants:
^ Event types:
^ seL4_InstructionBreakpoint.
^ seL4_DataBreakpoint.
^ seL4_SoftwareBreakRequest.
^ Access types:
^ seL4_BreakOnRead.
^ seL4_BreakOnWrite.
^ seL4_BreakOnReadWrite.
^ Exports:
^ seL4_NumHWBreakpoints.
^ seL4_NumExclusiveBreakpoints.
^ seL4_NumExclusiveWatchpoints.
^ seL4_NumDualFunctionMonitors.
^ seL4_FirstBreakpoint.
^ seL4_FirstWatchpoint.
^ seL4_FirstDualFunctionMonitor.

See documentation in the seL4 API manual.