There were two notable bugs:
- the maple transfer/data sizes were not being set correctly
- align_32byte always realigned the address of `_scene`, and not the
`mem` parameter as expected. This had the effect of the maple-DMA
send and receive buffers being the same buffer. On real hardware,
this causes unpredicable behavior.
This also includes an example for generating a quad primitive. In
flycast, this is very obviously rendered as two triangles. On real
hardware, this appears to be a "native" quad.
This rearranges scene.cpp to a file organization that more closely
follows which code is responsible for what area of (hardware)
initialization.
All TA and CORE register accesses now use the new ta_bits.h and
core_bits.h, respectively.
