imx: ventana: use stack relocation

Certain features we desire require a larger stack than is available by using
iRAM (most notably for us, env_mmc). Relocate the stack to DRAM so that
we can use these features.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/gwventana_defconfig b/configs/gwventana_defconfig
index c7882ac..2d6552f 100644
--- a/configs/gwventana_defconfig
+++ b/configs/gwventana_defconfig
@@ -3,3 +3,5 @@
 CONFIG_SYS_MALLOC_F=y
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6QDL"
+CONFIG_SPL_STACK_R=y
+CONFIG_SPL_STACK_R_ADDR=0x18000000