ARM: imx_v6_v7_defconfig: Enable SIOX bus

Now that there is a board making use of this bus is available
enable the siox code to increase compile coverage.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>