feat(plat/arm): add N2 CPU error injection support

N2 CPU allows error injections of Corrected Error (CE), Deferred Error
(DE) and Uncontainable Error (UC) using the Pseudo Fault Generation
register that are implmented by the N2 CPU ras extensions. Programming
these registers with valid values can generate error injections and help
in validating the error handling software.

In addition introduce the helper functions that are required to program
the CPU pseudo fault generation (PFG) registers. The PFG registers are
injection register and writing them initiates error injection on CPU.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I9d0682c3304e9e02feeeffb93386b58fa630af6a