Workaround for Cortex A76 erratum 1800710

Workaround for Cortex A76 erratum 1800710

Cortex A76 erratum 1800710 is a Cat B erratum, present in older
revisions of the Cortex A76 processor core.  The workaround is to
set a bit in the ECTLR_EL1 system register, which disables allocation
of splintered pages in the L2 TLB.

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: Ifc34f2e9e053dcee6a108cfb7df7ff7f497c9493