Another 10-bit packed YUV format

[Josh Doe]

I'm writing a source for Imperx SDI grabbers, and they seem to use a
format I've not seen before.

It's packed 4:2:2 YUV 10 bits per channel, YVYU order, big endian, and
with no padding bits, so they pack 4 components in 5 bytes, and each
row is aligned to 4 bytes. Unless others use this format, it's not
worth adding a new pixel format.

>From grepping plugins for similar formats, it seems v210 is the most
commonly supported format, so adding conversions internal to the
source to v210 and AYUV64 might make the most sense. Input welcome, I
don't often encounter new formats.

-Josh