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/espt_defconfig b/configs/espt_defconfig
index 5a83fe0..cda9da9 100644
--- a/configs/espt_defconfig
+++ b/configs/espt_defconfig
@@ -2,6 +2,8 @@
 CONFIG_TARGET_ESPT=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_BOOTDELAY=-1
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttySC0,115200 root=1f01"
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set