FIELD signal is used for indicating frame field type to the frame grabber
in interlaced scan mode, as specified in ITU-R BT.601 standard.
In normal operation mode FIELD = 0 selects Field1 (odd) and FIELD = 1
selects Field2 (even). When the FIELD signal is inverted it's the other
way around.

Add corresponding flags for configuring the FIELD signal polarity,
V4L2_MBUS_FIELD_EVEN_HIGH for the standard (non-inverted) case and
V4L2_MBUS_FIELD_EVEN_LOW for inverted case.

Also add a comment about usage of V4L2_MBUS_[HV]SYNC* flags for
the hardware that uses [HV]REF signals.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>