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/sansa_fuze_plus_defconfig b/configs/sansa_fuze_plus_defconfig
index 0da8d52..83fdca4 100644
--- a/configs/sansa_fuze_plus_defconfig
+++ b/configs/sansa_fuze_plus_defconfig
@@ -7,6 +7,8 @@
 CONFIG_VIDEO=y
 CONFIG_ENV_IS_NOWHERE=y
 CONFIG_BOOTDELAY=3
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="console=ttyAMA0,115200n8 "
 # CONFIG_CONSOLE_MUX is not set
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_VERSION_VARIABLE=y