wl1251: split wl251 platform data to a separate structure

Move the wl1251 part of the wl12xx platform data structure into a new
structure specifically for wl1251.  Change the platform data built-in
block and board files accordingly.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Sebastian Reichel <sre@debian.org>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: John W. Linville <linville@tuxdriver.com>