KVM: arm64: Expose ID_AA64PFR2_EL1 to userspace and guests

KVM: arm64: Expose ID_AA64PFR2_EL1 to userspace and guests

Everything is now in place for a guest to "enjoy" FP8 support.
Expose ID_AA64PFR2_EL1 to both userspace and guests, with the
explicit restriction of only being able to clear FPMR.

All other features (MTE* at the time of writing) are hidden
and not writable.

Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240820131802.3547589-9-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>