Cortex A76 erratum 1791580 is a Cat B erratum present in earlier
revisions of the Cortex A76. The workaround is to set a bit in the
implementation defined CPUACTLR2 register, which forces atomic store
operations to write-back memory to be performed in the L1 data cache.

This errata is explained in this SDEN:
https://static.docs.arm.com/sden885749/g/Arm_Cortex_A76_MP052_Software_Developer_Errata_Notice_v20.pdf

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: Iefd58159b3f2e2286138993317b98e57dc361925