Blackfin SPI driver: reconfigure speed_hz and bits_per_word in each spi transfer

 - reconfigure SPI baud from speed_hz of each spi transfer
 - according to spi_transfer.bits_per_word to reprogram register and setup
   correct SPI operation handlers

Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>