libplatsupport: Add GICv3 IRQ chip parser

This new parser module is able to parse interrupts under the format
specified by the GICv3 bindings. For now, the parser is only able to
parse SPI interrupts and not PPI interrupts.

platsupport: add new PER_CPU irq type

This is required so irqs can specify target cpus on arm.

libplatsupport: Add PS_INVALID_IRQ_ID constant

This adds a constant to represent a invalid IRQ IDs.

libplatsupport: irq_callback_t->irq_callback_fn_t

The IRQ interface's callback function type is of a function pointer. We
update the type's name to follow the style guide and to reflect the
actual functionality that the type represents.

libplatsupport: Add extra docs to IRQ interface

Some extra functionality was added to the callback-related mechanisms,
so the documentation is updated to reflect that.

trivial: Update irq.h license

libplatsupport: Add new IRQ interface

This commit adds the prototypes of the new IRQ interface. The interface
is intended to be implemented and extended by libsel4camkes and
libsel4platsupport.

libplatsupport: Remove unneeded header from irq.h

The contents of the header is not used at all in the file.

libplatsupport: Add 'other' IRQ type

This 'other' interrupt type is reserved for special instances of
interrupts. One such example would be PCI interrupts that are mapped to
the same interrupt number.

trivial: libplatsupport: style fixes

libplatsupport: Add IRQ type with trigger

Allow using IRQControl_GetTrigger in libsel4simple.

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