ARM: multi_v7_defconfig: Enable AHCI_IMX

The Wandboard Quad comes with a SATA port. Enable the IMX SATA driver by
default to make it easy to have the root filesystem on it.

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>