tegra: Fix build error in plutux, medcom

We need to define CONFIG_ENV_IS_NOWHERE to avoid this error:

cmd_nvedit.c:69:3: error: #error Define one of CONFIG_ENV_IS_IN_...

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/include/configs/medcom.h b/include/configs/medcom.h
index 6a54925..2dc3507 100644
--- a/include/configs/medcom.h
+++ b/include/configs/medcom.h
@@ -41,6 +41,8 @@
 
 #define CONFIG_BOARD_EARLY_INIT_F
 
+#define CONFIG_ENV_IS_NOWHERE
+
 /* SD/MMC */
 #define CONFIG_MMC
 #define CONFIG_GENERIC_MMC