arm64: sysreg: Migrate MDCR_EL2 definition to table

Migrate MDCR_EL2 over to the sysreg table and align definitions with
DDI0601 2024-09.

Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20241025182354.3364124-4-oliver.upton@linux.dev


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