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/at91sam9g20ek_dataflash_cs0_defconfig b/configs/at91sam9g20ek_dataflash_cs0_defconfig
index da86e8ce..b70c3f8 100644
--- a/configs/at91sam9g20ek_dataflash_cs0_defconfig
+++ b/configs/at91sam9g20ek_dataflash_cs0_defconfig
@@ -7,6 +7,8 @@
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,SYS_USE_DATAFLASH_CS0"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttyS0,115200 root=/dev/mtdblock0 mtdparts=atmel_nand:-(root) rw rootfstype=jffs2"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
 # CONFIG_CMD_BDI is not set