ArmPkg/ArmGicDxe: annotate protocol usage in "ArmGicDxe.inf"

ArmPkg/ArmGicDxe: annotate protocol usage in "ArmGicDxe.inf"

"ArmGicDxe.inf" currently does not document how the protocols in the
[Protocols] section are used. Such comments help us analyze behavior, so
let's add them now.

- gHardwareInterruptProtocolGuid and gHardwareInterrupt2ProtocolGuid are
  always produced on the InterruptDxeInitialize() -> (GicV2DxeInitialize()
  | GicV3DxeInitialize()) -> InstallAndRegisterInterruptService() call
  path.

- gEfiCpuArchProtocolGuid is consumed in the CpuArchEventProtocolNotify()
  protocol notify callback. (Technically this is "conditional"; however
  the firmware cannot work without architectural protocols, so we can call
  it unconditional.)

While at it, drop the gArmGicDxeFileGuid comment from FILE_GUID; we're
going to make that GUID uninteresting soon.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Supreeth Venkatesh <Supreeth.Venkatesh@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Steve Capper <steve.capper@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>