media: ti-vpe: Add support for SEQ_BT

SEQ_BT indicates the buffer for bottom field needs to be processed
before the top field.

Simplify the field selection logic to support SEQ_BT as well.

Modify the interlace flags to include any of alternate, SEQ_TB, SEQ_BT.
Update other format error checking to consider SEQ_BT.
Replace SEQ_TB with SEQ_XX wherever applicable.

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