KVM: arm64: nv: Apply guest's MDCR traps in nested context

KVM: arm64: nv: Apply guest's MDCR traps in nested context

KVM needs to ensure the guest hypervisor's traps take effect when the
vCPU is in a nested context. While supporting infrastructure is in place
for most of the EL2 trap registers, MDCR_EL2 is not.

Fold the guest's trap configuration into the effective MDCR_EL2. Apply
it directly to the in-memory representation as it gets recomputed on
every vcpu_load() anyway.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>