Blackfin arch: Fix bug - Run "reboot" hangs bf518-ezbrd

[Mike Frysinger <vapier.adi@gmail.com>:
 - setup P_DEFAULT_BOOT_SPI_CS  for every arch based on
   the default bootrom behavior and convert all our boards
   to it
 - revert previous anomaly change ... bf51x is not affected
   by anomaly 05000353]

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