Blackfin arch: DMA operation cleanup

1) Disable Interrupts during DMA memcpy to avoid raise conditions.
2) Mark MDMA channel 0 as reserved, since were using it internally.
3) Add DMA based equivalents for insX and outsX.
4) Our insX and outsX only handles len <= 2^16.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>