As we are introducing two new formats and supporting conversions
between them, and also with the existing 0rgb32/0bgr32 formats, we get
a combinatorial explosion of kernels. I introduced a few new macros to
keep the things mostly managable.

The conversions are all simple, following existing patterns, with four
specific exceptions. When converting from 0rgb32/0bgr32 to rgb32/bgr32,
we need to ensure the alpha value is set to 1. In all other cases, it
can just be passed through, either to be used or ignored.