drm/nouveau/disp: Add mechanism to convert HDMI InfoFrames to hardware format

HDMI InfoFrames are passed to NVKM as bags of bytes, but the
hardware needs them to be packed into words.  Rather than having
four (or more) copies of the packing logic introduce a single copy
now, in a central place.

We currently need these for AVI and Vendor InfoFrames, but we may
also expect to need them for Audio InfoFrames at some point.

Signed-off-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>