KVM: arm64: Replace vgic_v3_uaccess_read_pending with vgic_uaccess_read_pending

Now that GICv2 has a proper userspace accessor for the pending state,
switch GICv3 over to it, dropping the local version, moving over the
specific behaviours that CGIv3 requires (such as the distinction
between pending latch and line level which were never enforced
with GICv2).

We also gain extra locking that isn't really necessary for userspace,
but that's a small price to pay for getting rid of superfluous code.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20220607131427.1164881-3-maz@kernel.org