Blackfin arch: update defconfig file for all boards

Blackfin arch: update defconfig file for all boards

 - do not bother generating deprecated /sys files by default now since
   mdev does not need it
 - Don't built-in char sport driver and build it as a module in defconfig
 - disable CONFIG_DEVKMEM by default
 - enable spi flash driver on boards that have one
 - switch config to the NAND platfrom driver rather than the bfin async one
 - do not make BFIN_DMA_5XX optional since a large portion of our code relies
   on dma functions existing

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>