arm64/kvm: Fix bitrotted comment for SVE handling in handle_exit.c

The comment on the SVE trap handler in handle_exit.c says that it is a
placeholder until we support SVE in guests which we now do for both VHE
and nVHE cases so we really shouldn't get here in any sort of standard
case. Update the comment to be less immediately incorrect, the handling
of such a situation is correct.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211025163232.3502052-1-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>