KVM: arm64: Refactor kvm_vcpu_enable_ptrauth() for hyp use

Move kvm_vcpu_enable_ptrauth() to a shared header to be used by
hypervisor code in protected mode.

No functional change intended.

Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://lore.kernel.org/r/20241018074833.2563674-3-tabba@google.com


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>