Almost all of the features described by the ISA registers have no KVM
involvement. Allow userspace to change the value of these registers with
a couple exceptions:

 - MOPS is not writable as KVM does not currently virtualize FEAT_MOPS.

 - The PAuth fields are not writable as KVM requires both address and
   generic authentication be enabled.
Co-developed-by: Jing Zhang <jingzhangos@google.com>
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231003230408.3405722-7-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>