media: Documentation: v4l: Rework LP-11 documentation, add callbacks

Rework LP-11 and LP-111 mode documentation to make it more understandable
and useful. This involves adding pre_streamon and post_streamon callbacks
that make it possible to explicitly transition the transmitter to either
mode.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>