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/ms7720se_defconfig b/configs/ms7720se_defconfig
index 2e5ed21..762ddad 100644
--- a/configs/ms7720se_defconfig
+++ b/configs/ms7720se_defconfig
@@ -1,5 +1,7 @@
 CONFIG_SH=y
 CONFIG_TARGET_MS7720SE=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttySC0,115200"
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_AUTOBOOT is not set
 # CONFIG_CMD_BDI is not set