ARM: rockchip: rv1108: Add support for default distro_bootcmd

This allow easier integration of RV1108 based boards on generic
distributions and build systems.

To avoid behavior change, we make evb-rv1108 to use the existing
environment as it boots from its SPI NOR.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/include/configs/evb_rv1108.h b/include/configs/evb_rv1108.h
index 34739c7..b742d98 100644
--- a/include/configs/evb_rv1108.h
+++ b/include/configs/evb_rv1108.h
@@ -11,11 +11,14 @@
 /*
  * Default environment settings
  */
+#undef CONFIG_EXTRA_ENV_SETTINGS
 #define CONFIG_EXTRA_ENV_SETTINGS                                       \
 	"netdev=eth0\0"                                                 \
 	"ipaddr=172.16.12.50\0"                                         \
 	"serverip=172.16.12.69\0"					\
 	""
+
+#undef CONFIG_BOOTCOMMAND
 #define CONFIG_BOOTCOMMAND						\
 	"sf probe;"							\
 	"sf read 0x62000000 0x140800 0x500000;"				\