staging/wilc1000: move init/exit functions to driver files

The driver interfaces are in linux_wlan_sdio.c and linux_wlan_spi.c, so
this is where the init and exit functions should be. Splitting this up
enables further cleanups, including eventually allowing both modules
to be built together.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>