Platforms/RaspberryPi: Fix RPi4 GICC PMU PPI

Arm SBSA specification section ver 6.0, 4.1.5 defines specific PPI
values for certain standard interrupt IDs. The value for
"Performance Monitors Interrupt" needs to be 23.

REF: https://developer.arm.com/documentation/den0029/latest

This partially fixes SBSA test #11 ("Incorrect PPI value") reported in
https://github.com/pftf/RPi4/issues/74



Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Pete Batard <pete@akeo.ie>
Cc: Andrei Warkentin <awarkentin@vmware.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Samer El-Haj-Mahmoud <samer.el-haj-mahmoud@arm.com>
Reviewed-by: Pete Batard <pete@akeo.ie>