fix(cpus): workaround for Cortex-A715 erratum 2429384

Cortex-A715 erratum 2429384 is a cat B erratum that applies to
revision r1p0 and is fixed in r1p1. The workaround is to set
bit[27] of CPUACTLR2_EL1. There is no workaround for revision
r0p0.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN2148827/latest



Change-Id: I3cdb1b71567542174759f6946e9c81f77d0d993d
Signed-off-by: Bipin Ravi <biprav01@u203721.austin.arm.com>