options: add --deinterlace-field-parity option

Previously there was no way to specify the field order of interlaced videos
when deinterlacing with inbuilt filters. Lavfi deinterlacers seemed to prefer
top field order while inbuilt ones (vdpaupp, vavpp, d3d11vpp) seemed to prefer
bottom field order. The default "auto" option should work exactly as before
while specifying either "tff" or "bff" should force the specified field order