[TF-A] [MPAM] Removing initialization of MPAM EL2 registers when EL2 is used

Hi all,

The small patch below [1] removes initialization of MPAM EL2 registers when EL2 is used, with the assumption that if an EL2 software exists it should perform the necessary initializations. Please take a look at the patch and let me know if this change affects any downstream projects.

Thanks! Zelalem

[1] https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/13805/7