feat(cpus): conform DSU errata to errata framework PCS

Errata framework expects workarounds to clobber x0 to x8 and checker
functions to clobber x0-x4.

Update DSU errata functions to adhere to the standard, which is documented
here: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/19295.

Signed-off-by: Kathleen Capella <kathleen.capella@arm.com>
Change-Id: Ie0e492473ab8b2bee4335b6b1db00796fabdd59d
1 file changed