media: dmxdev: drop unneeded <linux/kernel.h> inclusion from other headers

There is no evidence we need kernel.h inclusion in certain headers.
Drop unneeded <linux/kernel.h> inclusion from other headers.

Link: https://lore.kernel.org/linux-media/20211210120201.35635-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

media: dmxdev: Fix the logic that enables DMA mmap support

Some conditions required for DVB mmap support to work are reversed.
Also, the logic is not too clear.

So, improve the logic, making it easier to be handled.

PS.: I'm pretty sure that I fixed it while testing, but, somehow,
the change got lost.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

media: dvb kAPI docs: document dvb_vb2.h

Document the data structures and functions inside this kAPI header.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

media: move dvb kAPI headers to include/media

Except for DVB, all media kAPI headers are at include/media.

Move the headers to it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>