KVM: arm64: Hoist MTE validation check out of MMU lock path

KVM: arm64: Hoist MTE validation check out of MMU lock path

Simplify the non-cacheable attributes assignment by using a ternary
operator. Additionally, hoist the MTE validation check (mte_allowed) out
of kvm_s2_fault_map() and into kvm_s2_fault_compute_prot(). This allows
us to fail faster and avoid acquiring the KVM MMU lock unnecessarily
when the VMM introduces a disallowed VMA for an MTE-enabled guest.

Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>