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/M53017EVB_defconfig b/configs/M53017EVB_defconfig
index 67dfe0b..b5caeed 100644
--- a/configs/M53017EVB_defconfig
+++ b/configs/M53017EVB_defconfig
@@ -3,6 +3,8 @@
 CONFIG_TARGET_M53017EVB=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_BOOTDELAY=1
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/mtdblock3 rw rootfstype=jffs2"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="-> "
 # CONFIG_CMD_SETEXPR is not set