KVM: arm64: nv: Add kvm_has_pauth() helper

KVM: arm64: nv: Add kvm_has_pauth() helper

Pointer Authentication comes in many flavors, and a faithful emulation
relies on correctly handling the flavour implemented by the HW.

For this, provide a new kvm_has_pauth() that checks whether we
expose to the guest a particular level of support. This checks
across all 3 possible authentication algorithms (Q5, Q3 and IMPDEF).

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-12-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>