common: Move CONFIG_BOOTARGS to Kconfig

Also introduce CONFIG_USE_BOOTARGS option so we can control if
CONFIG_BOOTARGS defined at all.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
[trini: Resync r8a779[56]_ulcb, various ls10xx targets]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/env_default.h b/include/env_default.h
index acd4198..b574345 100644
--- a/include/env_default.h
+++ b/include/env_default.h
@@ -28,7 +28,7 @@
 #ifdef	CONFIG_ENV_FLAGS_LIST_DEFAULT
 	ENV_FLAGS_VAR "=" CONFIG_ENV_FLAGS_LIST_DEFAULT "\0"
 #endif
-#ifdef	CONFIG_BOOTARGS
+#ifdef	CONFIG_USE_BOOTARGS
 	"bootargs="	CONFIG_BOOTARGS			"\0"
 #endif
 #ifdef	CONFIG_BOOTCOMMAND