dev-arm: Check EnableLPIs before checking for pending LPIs

dev-arm: Check EnableLPIs before checking for pending LPIs

Before reading the tables, GICR_PENDBASER and GICR_PROPBASER need to be
properly set, and those will have a consistent value only once sw
enables LPIs.

Change-Id: Ifb87944a491045e7a13ce7a280c555cb0c1e47f4
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18592
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>