dev-arm: Gicv3 maintenance interrupt never cleared

dev-arm: Gicv3 maintenance interrupt never cleared

The maintenance interrupt is a level sensitive interrupt though it has
been treated as edge triggered so far.

In order to be level sensitive, it needs to be cleared once the condition
which led to its generation are not valid anymore.

Change-Id: I9af9f4bf27622a7961393b00a145d6c9835d738b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31614
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>