V4L/DVB (12896): ISDB-T: add mapping of LAYER_ENABLED to frontend-cache

It was forgotten to map the LAYER_ENABLED ioctl to the frontend-cache and back.

Signed-off-by: Patrick Boettcher <pboettcher@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>