media: CEC: keep related menu entries together

Keep all of the CEC menu items grouped together.
By grouping all of these menu entries inside a menu/endmenu block,
they are forced to be kept together and they are displayed/presented
in a group for users.

Tested with xconfig, gconfig, menuconfig, and nconfig.

Fixes: 46d2a3b9 ("media: place CEC menu before MEDIA_SUPPORT")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>