fix(errata): workaround for Cortex-X2 errata 2017096

Cortex-X2 erratum 2017096 is a Cat B erratum that applies to
revisions r0p0, r1p0 & r2p0. The workaround is to set CPUECLTR_EL1[8]
to 1 which disables store issue prefetching.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1775100



Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
Change-Id: I3b740aedc95c2394f6b8d1186014d2b2f640ae05