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/integratorap_cm720t_defconfig b/configs/integratorap_cm720t_defconfig
index 349bdcd..d103792 100644
--- a/configs/integratorap_cm720t_defconfig
+++ b/configs/integratorap_cm720t_defconfig
@@ -3,6 +3,8 @@
 CONFIG_ARCH_INTEGRATOR_AP=y
 CONFIG_CM720T=y
 CONFIG_ENV_IS_NOWHERE=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/mtdblock0 console=ttyAM0 console=tty"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y