[WATCHDOG] Blackfin Watchdog Driver: split platform device/driver

 - split platform device/driver registering from actual watchdog device/driver
   registering so that we can cleanly load/unload
 - fixup __initdata with __initconst and __devinitdata with __devinitconst

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>