cpu: IntrControl, clear all and check helpers

cpu: IntrControl, clear all and check helpers

This patch extends the IntrControl to provided additional member
functions for (1) clearing all pending interrupts in a PE and (2)
checking for any pending interrupt in a PE. These are intended to
be used from interrupt management related peripherals.

Change-Id: I06b553872ed469e7449b872a0716865773ace154
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26809
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>