KVM: arm64: Provide sanitized mmfr* registers at EL2

We will need to read sanitized values of mmfr{0,1}_el1 at EL2 soon, so
add them to the list of copied variables.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-35-qperret@google.com