staging: wilc1000: linux_wlan_spi.c: move all the codes to wilc_spi.c

This patch moves all the codes in linux_wlan_spi.c to wilc_spi.c to make
one spi module. Make wilc_spi_tx, wilc_spi_rx and wilc_spi_tx_rx static
functions. Remove function declaration in linux_wlan_spi.h, which is unnedded
now. No modification has been made inside the codes.
linux_wlan_spi.[ch] will be remove in the next patch.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>