fix(cpus): workaround for Cortex-X4 erratum 2740089

Cortex-X4 erratum 2740089 is a Cat B erratum that applies to
all revisions <=r0p1 and is fixed in r0p2. The workaround is to
insert a dsb before the isb in the power down sequence.

SDEN documentation:
https://developer.arm.com/documentation/SDEN2432808/latest

Change-Id: I1d0fa4dd383437044a4467591f65a4a8514cabdc
Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
3 files changed