KVM: arm64: Prevent userspace from handling SMC64 arch range

KVM: arm64: Prevent userspace from handling SMC64 arch range

Though presently unused, there is an SMC64 view of the Arm architecture
calls defined by the SMCCC. The documentation of the SMCCC filter states
that the SMC64 range is reserved, but nothing actually prevents
userspace from applying a filter to the range.

Insert a range with the HANDLE action for the SMC64 arch range, thereby
preventing userspace from imposing filtering/forwarding on it.

Fixes: fb88707dd39b ("KVM: arm64: Use a maple tree to represent the SMCCC filter")
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230408121732.3411329-2-oliver.upton@linux.dev