Rather than reinventing the wheel in KVM to do ID register sanitisation
we can rely on the work already done in the core kernel. Implement a
generalized sanitisation of ID registers based on the combination of the
arm64_ftr_bits definitions from the core kernel and (optionally) a set
of KVM-specific overrides.

This all amounts to absolutely nothing for now, but will be used in
subsequent changes to realize user-configurable ID registers.
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Link: https://lore.kernel.org/r/20230609190054.1542113-8-oliver.upton@linux.dev
[Oliver: split off from monster patch, rewrote commit description,
 reworked RAZ handling, return EINVAL to userspace]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>