fix(cpus): workaround for Cortex-A710 erratum 1901946

Cortex-A710 erratum 1901946 is a Cat B erratum that applies
to revision r1p0 and is fixed in r2p0.

The workaround is to set CPUACTLR4_EL1[15]. This has a slight
performance impact.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1775101

Change-Id: I703f0e6ee122e44a9bc284d90f1465039e3b40e4
Signed-off-by: John Powell <john.powell@arm.com>
4 files changed