Based on a patch by qyot27. Add the missing parts in mp_get_chroma_shift(),
which allow allocation of such images, and which make vo_opengl
automatically accept the new formats. Change the IMGFMT_IS_YUVP16_LE/BE
macros to properly report IMGFMT_444P14 as supported: this pixel format
has the highest numerical bit width identifier (0x55), which is not
covered by the mask ~0xfc. Remove 1 bit from the mask (makes it 0xf8) so
that IMGFMT_IS_YUVP16(IMGFMT_444P14) is 1. This is slightly risky, as
the organization of the image format IDs (actually FourCCs + mplayer
internal IDs) is messy at best, but it should be ok.