arm64/gcs: Flush the GCS locking state on exec

arm64/gcs: Flush the GCS locking state on exec

When we exec a new task we forget to flush the set of locked GCS mode bits.
Since we do flush the rest of the state this means that if GCS is locked
the new task will be unable to enable GCS, it will be locked as being
disabled. Add the expected flush.

Fixes: fc84bc5378a8 ("arm64/gcs: Context switch GCS state for EL0")
Cc: <stable@vger.kernel.org> # 6.13.x
Reported-by: Yury Khrustalev <Yury.Khrustalev@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Tested-by: Yury Khrustalev <yury.khrustalev@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>