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/stm32f429-discovery_defconfig b/configs/stm32f429-discovery_defconfig
index f16ca37..bff1b1b 100644
--- a/configs/stm32f429-discovery_defconfig
+++ b/configs/stm32f429-discovery_defconfig
@@ -4,6 +4,8 @@
 CONFIG_TARGET_STM32F429_DISCOVERY=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttyS0,115200 earlyprintk consoleblank=0 ignore_loglevel"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y