wl12xx: add driver

wl12xx is a driver for TI wl1251 802.11 chipset designed for embedded
devices, supporting both SDIO and SPI busses. Currently the driver
supports only SPI. Adding support 1253 (the 5 GHz version) should be
relatively easy. More information here:

http://focus.ti.com/general/docs/wtbu/wtbuproductcontent.tsp?contentId=4711&navigationId=12494&templateId=6123

(Collapsed original sequence of pre-merge patches into single commit for
initial merge. -- JWL)

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>