fix(errata): workaround for Cortex-A710 erratum 2147715

fix(errata): workaround for Cortex-A710 erratum 2147715

Cortex-A710 erratum 2147715 is a Cat B erratum that applies
to revision r2p0 of the CPU, and is fixed in r2p1. The work-
around is to set CPUACTLR_EL1[22]=1. Setting this will cause
the CFP instruction to invalidate all branch predictor resources
regardless of the context.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1775101/latest

Signed-off-by: Akram Ahmad <Akram.Ahmad@arm.com>
Change-Id: I94771bc1fc9b65a0c17d75200ec2b1df8a3279c6