tegra: enable CONFIG_ENV_VARS_UBOOT_CONFIG

So that all Tegra boards define environment variables that describe
themselves.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

include/configs/tegra2-common.h

@@ -68,6 +68,7 @@
 #endif
 
 /* Environment */
+#define CONFIG_ENV_VARS_UBOOT_CONFIG
 #define CONFIG_ENV_SIZE			0x2000	/* Total Size Environment */
 
 /*