poweprc/km82xx: add board specific environment variable

On mgcoge3ne a new environment variable bobcatreset is used.
So this patch adds a possibility to add board specific
environment variables in general and this specific variable
for mgcoge3ne.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
diff --git a/include/configs/mgcoge.h b/include/configs/mgcoge.h
index 93a6f4a..0745855 100644
--- a/include/configs/mgcoge.h
+++ b/include/configs/mgcoge.h
@@ -85,6 +85,8 @@
 			 PSDMR_CL_2)
 
 
+#define CONFIG_KM_BOARD_EXTRA_ENV	""
+
 /* include further common stuff for all keymile 82xx boards */
 #include "km82xx-common.h"