staging: wilc1000: remove wilc_wlan.c included in wilc_wfi_cfgoperations.c

This patch removes "wilc_wlan.c" from the wilc_wfi_cfgoperation.c file and
adds wilc_wlan.o into Makefile to compile it because there is few benefits.
This patch also adds "wilc_wfi_netdevice.h" in the wilc_wlan.c file to avoid
the compile errors.

Signed-off-by: Tony Cho <tony.cho@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>