media: docs: split cx2341x.rst into different audiences

This file contains both driver develompent documentation
(basically, firmware documentation) and IVTV-specific
documentation about VBI and raw formats, focused on uAPI
development.

Split on two, as they're usually read by different audiences.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>