crypt: bfin_crc - Remove useless SSYNC instruction and cache flush to DMA coherent memory

1) SSYNC instruction is blackfin specific and takes no effect in this driver.
2) DMA descriptor and SG middle buffer are in DMA coherent memory. No need
to flush.
3) Turn kzalloc, ioremap and request_irq into managed device APIs respectively.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>