wireless/wl12xx/wl1251: move TI WLAN modules to a common ti subdirectory

Move wl12xx and wl1251 modules into a new drivers/net/wireless/ti
directory.  Add a TI WLAN Kconfig option and Makefile to support this
change.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Cc: John W. Linville <linville@tuxdriver.com>