configs: add Freescale i.MX6 SoloX Sabre SD support

The i.MX6 SoloX SABRE board for smart devices is Freescale's reference design
board based on the heterogeneous ARM Cortex-A9 + Cortex-M4 i.MX6 SoloX
applications processor.

This defconfig is inspired from previous freescale_imx6*sabresd_defconfig, and
is based on Freescale "official" git repo on git.freescale.com and SW release
3.10.53_1.1.0_ga.

Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Gary Bisson <bisson.gary@gmail.com>
Cc: Jérôme Pouiller <jezz@sysmic.org>
Cc: Gilles Talis <gilles.talis@gmail.com>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>