KVM: arm64: nv: Add trap forwarding for MDCR_EL2

Describe the MDCR_EL2 register, and associate it with all the sysregs
it allows to trap.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Jing Zhang <jingzhangos@google.com>
Link: https://lore.kernel.org/r/20230815183903.2735724-18-maz@kernel.org