configs: add Freescale SABRE-SD board support

SABRE Board for Smart Devices (SABRE-SD) is Freescale's evaluation board
based on the i.MX 6Quad ARM Cortex-A9 applications processor.

This defconfig is based off Freescale "official" git repo on git.freescale.com
and SW release 3.0.35_4.1.0.

[Peter: add comments to defconfig]
Signed-off-by: Gilles Talis <gilles.talis@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>