platform/chrome: cros_ec_lpc - Include linux/io.h header file

The driver uses the inb() and outb() I/O functions so should
include the header file that has these functions definitions.

This patch fixes the following error when the header is not
explicitly included:

drivers/platform/chrome//cros_ec_lpc.c: In function ‘ec_response_timed_out’:
drivers/platform/chrome//cros_ec_lpc.c:40:3: error: implicit declaration of function ‘inb’ [-Werror=implicit-function-declaration]
drivers/platform/chrome//cros_ec_lpc.c: In function ‘cros_ec_cmd_xfer_lpc’:
drivers/platform/chrome//cros_ec_lpc.c:75:3: error: implicit declaration of function ‘outb’ [-Werror=implicit-function-declaration]

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Olof Johansson <olof@lixom.net>