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/configs/M54451EVB_stmicro_defconfig b/configs/M54451EVB_stmicro_defconfig
index 0f7a87c..ddded43 100644
--- a/configs/M54451EVB_stmicro_defconfig
+++ b/configs/M54451EVB_stmicro_defconfig
@@ -4,6 +4,8 @@
 CONFIG_SYS_EXTRA_OPTIONS="CF_SBF,SYS_STMICRO_BOOT,SYS_INPUT_CLKSRC=24000000"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_BOOTDELAY=1
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/mtdblock1 rw rootfstype=jffs2 ip=none mtdparts=physmap-flash.0:2M(kernel)ro,-(jffs2)"
 # CONFIG_CMD_LOADB is not set
 # CONFIG_CMD_LOADS is not set
 CONFIG_CMD_SF=y