KVM: arm64: nv: Handle VNCR_EL2-triggered faults

As VNCR_EL2.BADDR contains a VA, it is bound to trigger faults.

These faults can have multiple source:

- We haven't mapped anything on the host: we need to compute the
  resulting translation, populate a TLB, and eventually map
  the corresponding page

- The permissions are out of whack: we need to tell the guest about
  this state of affairs

Note that the kernel doesn't support S1POE for itself yet, so
the particular case of a VNCR page mapped with no permissions
or with write-only permissions is not correctly handled yet.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250514103501.2225951-10-maz@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>