ArmPkg/Drivers/ArmGicDxe: Add ESPI support for GICv3

[NicholasGraves]

• Add ESPI configuration to GICv3.
• Remove mNumGicInterrupts and replace with GicIsValidSource(), GicGetGreatestIntid() APIs. mNumGicInterrupts is still used internally in GICv2.
• Tested on qemu with the BSA test suite.

Description

Adds ESPI support to GICv3
#10869

• Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Tested on qemu with ESPI support via the BSA ACS test suite.

Integration Instructions

N/A

[leiflindholm]

Thanks for this, it's definitely a gap that needs closing.

I'll do a more detailed review later today, but two high-level comments:

• ESPI is a heavily clashing acronym. This is probably why the GIC ARM consistently refers to it as Extended SPI. I think that would be helpful to do here too.
• Is there any way to break this up into a few more commits? Bullet points in commit messages frequently indicate there is.

[NicholasGraves]

Thanks for this, it's definitely a gap that needs closing.

I'll do a more detailed review later today, but two high-level comments:

• ESPI is a heavily clashing acronym. This is probably why the GIC ARM consistently refers to it as Extended SPI. I think that would be helpful to do here too.
• Is there any way to break this up into a few more commits? Bullet points in commit messages frequently indicate there is.

Changed ESPI -> ExtSpi in code and extended SPI in comments.

I don't think it's possible to easily break this up into atomic changes that are all functional.