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/M54418TWR_nand_rmii_defconfig b/configs/M54418TWR_nand_rmii_defconfig
index 6abe98a..b863422 100644
--- a/configs/M54418TWR_nand_rmii_defconfig
+++ b/configs/M54418TWR_nand_rmii_defconfig
@@ -3,6 +3,8 @@
 CONFIG_TARGET_M54418TWR=y
 CONFIG_SYS_EXTRA_OPTIONS="SYS_NAND_BOOT,SYS_INPUT_CLKSRC=50000000"
 CONFIG_ENV_IS_NOWHERE=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/mtdblock2 rw rootfstype=jffs2 mtdparts=NAND:1M(u-boot)ro,7M(kernel)ro,-(jffs2) console=ttyS0,115200"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="-> "