KVM: arm64: Describe SCTLR2_ELx RESx masks

External abort injection will soon rely on a sanitised view of
SCTLR2_ELx to determine exception routing. Compute the RESx masks.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-15-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>