wl1251: register platform_device to pass board data

wl1251 is embedded chip that can be connected using SDIO bus, and is not
an actual SDIO card. For this reason there is a need to pass some board
specific data, like 'EEPROM is attached' flag or power control callback.

However currently there is no way to pass this data through SDIO subsystem,
so this patch registers dummy platform_device to allow that, until we
have a better solution to this.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Acked-by: Kalle Valo <kvalo@adurom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>