media: v4l2-core: add v4l2_debugfs_if_alloc/free()

Add new helpers to export received or transmitted HDMI InfoFrames to
debugfs.

This complements similar code in drm where the transmitted HDMI infoframes
are exported to debugfs.

The same names have been used as in drm, so this is consistent.

The exported infoframes can be parsed with the edid-decode utility.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>