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/rsk7264_defconfig b/configs/rsk7264_defconfig
index f1999b5..9a1db16 100644
--- a/configs/rsk7264_defconfig
+++ b/configs/rsk7264_defconfig
@@ -1,6 +1,8 @@
 CONFIG_SH=y
 CONFIG_TARGET_RSK7264=y
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttySC3,115200"
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_SCIF_CONSOLE=y