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/doc/README.x86 b/doc/README.x86
index 8025485..c542a69 100644
--- a/doc/README.x86
+++ b/doc/README.x86
@@ -792,11 +792,7 @@
 You can also bake this behaviour into your build by hard-coding the
 environment variables if you add this to minnowmax.h:
 
-#undef CONFIG_BOOTARGS
 #undef CONFIG_BOOTCOMMAND
-
-#define CONFIG_BOOTARGS		\
-	"root=/dev/sda2 ro"
 #define CONFIG_BOOTCOMMAND	\
 	"ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \
 	"ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \
@@ -805,6 +801,10 @@
 #undef CONFIG_EXTRA_ENV_SETTINGS
 #define CONFIG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}"
 
+and change CONFIG_BOOTARGS value in configs/minnowmax_defconfig to:
+
+CONFIG_BOOTARGS="root=/dev/sda2 ro"
+
 Test with SeaBIOS
 -----------------
 SeaBIOS [14] is an open source implementation of a 16-bit x86 BIOS. It can run