Use memcpy_{from,to}io() to read and write entire parameter RAM
slots, saving a surprising 268 bytes over the existing code.
Renames those parameters to be more sensible than "temp".

Fix a minor glitch and ensure all DMA channels are initialized with
a dummy transfer with all options zeroed, so it's not possible to
accidentally start getting intermediate completion callbacks or
event chaining by accident.  Save eight bytes while doing that.

Shrink davinci_stop_dma() by not testing if the bits are already
cleared; if they were, clearing again is harmless.  And shrink
map_dmach_queue() by avoiding a superfluous test.

EDMA runtime code footprint is now under 2700 bytes, and there
are still further cleanups that could be done...
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>