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/r8a7796_salvator-x_defconfig b/configs/r8a7796_salvator-x_defconfig
index 67f1466..06f8452 100644
--- a/configs/r8a7796_salvator-x_defconfig
+++ b/configs/r8a7796_salvator-x_defconfig
@@ -7,6 +7,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="r8a7796-salvator-x"
 CONFIG_SMBIOS_PRODUCT_NAME=""
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttySC0,115200 rw root=/dev/nfs nfsroot=192.168.0.1:/export/rfs ip=192.168.0.20"
 CONFIG_DEFAULT_FDT_FILE="r8a7796-salvator-x.dtb"
 CONFIG_VERSION_VARIABLE=y
 CONFIG_CMD_BOOTZ=y