KVM: arm64: Constraint PAuth support to consistent implementations

KVM: arm64: Constraint PAuth support to consistent implementations

PAuth comes it two parts: address authentication, and generic
authentication. So far, KVM mandates that both are implemented.

PAuth also comes in three flavours: Q5, Q3, and IMPDEF. Only one
can be implemented for any of address and generic authentication.

Crucially, the architecture doesn't mandate that address and generic
authentication implement the *same* flavour. This would make
implementing ERETAx very difficult for NV, something we are not
terribly keen on.

So only allow PAuth support for KVM on systems that are not totally
insane. Which is so far 100% of the known HW.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-4-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>