KVM: arm64: Correctly identify executable PTEs at stage-2

KVM: arm64: Correctly identify executable PTEs at stage-2

KVM invalidates the I-cache before installing an executable PTE on
implementations without DIC. Unfortunately, support for FEAT_XNX
broke this check as KVM_PTE_LEAF_ATTR_HI_S2_XN was expanded to a
bitfield.

Fix it by reusing kvm_pgtable_stage2_pte_prot() and testing the abstract
permission bits instead.

Fixes: 2608563b466b ("KVM: arm64: Add support for FEAT_XNX stage-2 permissions")
Reported-by: Sashiko (gemini/gemini-3.1-pro-preview)
Signed-off-by: Oliver Upton <oupton@kernel.org>
Reviewed-by: Wei-Lin Chang <weilin.chang@arm.com>
Link: https://patch.msgid.link/20260602165901.52800-3-oupton@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org