RAS: Allow individual interrupt registration

RAS: Allow individual interrupt registration

EHF currently allows for registering interrupt handlers for a defined
priority ranges. This is primarily targeted at various EL3 dispatchers
to own ranges of secure interrupt priorities in order to delegate
execution to lower ELs.

The RAS support added by earlier patches necessitates registering
handlers based on interrupt number so that error handling agents shall
receive and handle specific Error Recovery or Fault Handling interrupts
at EL3.

This patch introduces a macro, RAS_INTERRUPTS() to declare an array of
interrupt numbers and handlers. Error handling agents can use this macro
to register handlers for individual RAS interrupts. The array is
expected to be sorted in the increasing order of interrupt numbers.

As part of RAS initialisation, the list of all RAS interrupts are sorted
based on their ID so that, given an interrupt, its handler can be looked
up with a simple binary search.

For an error handling agent that wants to handle a RAS interrupt,
platform must:

  - Define PLAT_RAS_PRI to be the priority of all RAS exceptions.

  - Enumerate interrupts to have the GIC driver program individual EL3
    interrupts to the required priority range. This is required by EHF
    even before this patch.

Documentation to follow.

Change-Id: I9471e4887ff541f8a7a63309e9cd8f771f76aeda
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>