media: ti-vpe: Add support for NV21 format

In NV21 format, the chroma plane is written to memory such that the U
and V components are swapped for NV12.

Create a new entry in the VPDMA formats to describe the correct data
types used in the data descriptors.

Update all checks for NV12 and add NV21 there as well.

Add support for V4L2_PIX_FMT_NV21 format for both capture and output
streams.

Signed-off-by: Nikhil Devshatwar <nikhil.nd@ti.com>
Signed-off-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>