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/ds414_defconfig b/configs/ds414_defconfig
index 3f75a83..5cc0297 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -10,6 +10,8 @@
 CONFIG_DEFAULT_DEVICE_TREE="armada-xp-synology-ds414"
 CONFIG_DEBUG_UART=y
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttyS0,115200"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SPL=y
 CONFIG_SPL_I2C_SUPPORT=y