Up until now, we inlined lowres_flag as well as is_mpeg12
independently (unless CONFIG_SMALL was true); this commit
changes this to instead inline mpv_reconstruct_mb_internal()
(at most) four times, namely once for encoders, once for decoders
using lowres and once for non-lowres mpeg-1/2 decoders and once
for non-lowres non-mpeg-1/2 decoders (mpeg-1/2 is not inlined
in case of CONFIG_SMALL). This is neutral performance-wise,
but proved beneficial size-wise: It saved 1776B of .text
for GCC 11 or 1344B for Clang 14 (both -O3 x64).
Notice that inlining is_mpeg12 for is_encoder would not really
be beneficial, as the encoder codepath does mostly not depend
on is_mpeg12 at all.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>