KVM: arm64: Allow userspace to change ID_AA64MMFR{0-2}_EL1

Allow userspace to modify the guest-visible values of these ID
registers. Prevent changes to any of the virtualization features until
KVM picks up support for nested and we have a handle on managing NV
features.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
[oliver: prevent changes to EL2 features for now]
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231003230408.3405722-8-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>