Although KVM couples API and APK for simplicity, the architecture
makes no such requirement, and the two can be independently set or
cleared.

Check for which of the two possible reasons we have trapped here,
and if the corresponding L1 control bit isn't set, delegate the
handling for forwarding.

Otherwise, set this exact bit in HCR_EL2 and resume the guest.
Of course, in the non-NV case, we keep setting both bits and
be done with it. Note that the entry core already saves/restores
the keys should any of the two control bits be set.

This results in a bit of rework, and the removal of the (trivial)
vcpu_ptrauth_enable() helper.
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-10-maz@kernel.orgSigned-off-by: Marc Zyngier <maz@kernel.org>