This way a caller doesn't need to implement the logic for which (and how
many) tokens to write out to stuff one macroblock worth of EOBs. Make
the actual function implementations static, since they are now only used
in tokenize.c; also do some minor stylistic changes so it follows the
style guide a little more closely; use PLANE_TYPE where appropriate,
remove old (stale) frame_type function arguments; hardcode plane type
where only a single one is possible (2nd order DC or U/V EOB stuffing);
support stuffing 8x8/4x4 transform EOBs with no 2nd order DC.

Change-Id: Ia448e251d19a4e3182eddeb9edd034bd7dc16fa3