KVM: arm64: unify the tests for VMAs in memslots when MTE is enabled

Previously we allowed creating a memslot containing a private mapping that
was not VM_MTE_ALLOWED, but would later reject KVM_RUN with -EFAULT. Now
we reject the memory region at memslot creation time.

Since this is a minor tweak to the ABI (a VMM that created one of
these memslots would fail later anyway), no VMM to my knowledge has
MTE support yet, and the hardware with the necessary features is not
generally available, we can probably make this ABI change at this point.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221104011041.290951-7-pcc@google.com