Arm64/GicV3: Change default cache mode from GITS_BASER_CACHE_WAWB to GITS_BASER_CACHE_RAWAWB

For not yet determined reasons, the Qualcom Snapdragon Elite will
take no other value than RAWAWB, but we're basically OK with that,
because that should be the most performant setting. Investigations
are continuing.

This patch makes the Lenovo T14sGen6 laptop to boot to multiuser,
but very little else works.