This renames two parameter RAM calls that read and write entire param
sets, and re-focusses their descriptions on the fact that they update
parameter RAM.  That has nothing *directly* to do with any hardware DMA
channel.  Switch to unsigned params, letting some error checks be removed.

It also starts updating the dma.c comments to reflect the different
structural blocks of the programming interface, calling out the two
groups of parameter RAM operations and channel control operations.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>