fix(cpus): workaround for Cortex-A510 erratum 2666669

Cortex-A510 erratum 2666669 applies to revisions r1p1 and lower,
and is fixed in r1p2. The errata is mitigated by setting
IMP_CPUACTLR_EL1[38] to 1.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1873351/latest
https://developer.arm.com/documentation/SDEN1873361/latest



Signed-off-by: Akram Ahmad <Akram.Ahmad@arm.com>
Change-Id: Ief27e4a155e43e75f05f2710d0c7bd5da2dec43f