videodevice: handle NV12 <-> NM12 translation
videodevice: handle NV12 <-> NM12 translation

V4L2 and DRM differ in their interpretation of YUV420::NV12

V4L2 NV12 is a Y and UV co-located planes in a single plane buffer.

DRM NV12 is a Y and UV planes presented as dual plane buffer, which is
known as NM12 in V4L2.

Since here we have hybrid DRM/V4L2 user space helper functions we need
to translate DRM::NV12 to V4L2:NM12 pixel format back and forth to keep
the data view consistent.

Signed-off-by: Benoit Parrot <bcb9a852e31dc5481c193d9747d409fab944c767@ti.com>

tomba/kmsxx,tomba/kmsxx,tomba/kmsxx,tomba/kmsxx