mx6: Use a common SPL configuration file

Many boards use a minimal .cfg file in the SPL case.

Introduce spl_sd.cfg so that we can reuse it.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano Babic <sbabic@denx.de>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index 50c06f7..3c0d64f 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -1,4 +1,4 @@
 CONFIG_SPL=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/compulab/cm_fx6/imximage.cfg,MX6QDL,SPL"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6QDL,SPL"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_CM_FX6=y