Silicon/Broadcom/Bcm283x: Add interrupt driver

This currently only implements support for the architected timer
interrupts on the per-CPU interrupt controllers.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>