arm64/sve: KVM: Treat guest SVE use as undefined instruction execution

When trapping forbidden attempts by a guest to use SVE, we want the
guest to see a trap consistent with SVE not being implemented.

This patch injects an undefined instruction exception into the
guest in response to such an exception.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>