[Blackfin] arch: fix bug when DMA operation related core B of BF561

- Before DMA'ing data to core B L1 memory, caches have to be flushed.
- Before DMA'ing data from core B L1 memory, caches have to be invalidated.
- Fix lock/unlock.

Signed-off-by: Enrik Berkhan <Enrik.Berkhan@ge.com>
Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>