KVM: arm64: Wire up SCTLR2_ELx sysreg descriptors

Set up the sysreg descriptors for SCTLR2_ELx, along with the associated
storage and VNCR mapping.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250708172532.1699409-12-oliver.upton@linux.dev


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