Certain codecs seem to use a Surface with Bpp 2, but do not have any proper
format description. Whoever is maintaining these should check this commit and
fix the format properly.
MKID_BE relied on unspecified behavior of the C++ compiler,
and as such was always a bit unsafe. The new MKTAG macro
is slightly less elegant, but does no longer depend on the
behavior of the compiler.
Inspired by FFmpeg, which has an almost identical macro.