udoo_neo: Fixes for booting from the mSD card

This fixes booting from the mSD card from both SPL and when
using it for the OS booting. It also cleans up a few mmc
booting bits that are no longer needed.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/udoo_neo_defconfig b/configs/udoo_neo_defconfig
index b2a3e9b..f01d2e2 100644
--- a/configs/udoo_neo_defconfig
+++ b/configs/udoo_neo_defconfig
@@ -35,6 +35,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_SYS_MMC_ENV_DEV=1
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_SYS_I2C_LEGACY=y