20C: Enable HDMA transfers

<P>There are 8 DMA channels, numbered 0 to 7.&nbsp; Simply replace the
question mark with the number of the channel you want to use.&nbsp; Each
channel can be used independently of the others.

<P>There are two basic types of DMA: DMA and HDMA.&nbsp; Normal DMA is
quite straightforward. The SNES program simply puts a source address into
$43?2, a destination address into $43?1 and the number of bytes to copy
into $43?5.&nbsp; The reason $43?1 is only a one-byte register is because