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/qemu-x86_64_defconfig b/configs/qemu-x86_64_defconfig
index 44a1536..8d55588 100644
--- a/configs/qemu-x86_64_defconfig
+++ b/configs/qemu-x86_64_defconfig
@@ -18,6 +18,8 @@
 CONFIG_SPL_LOAD_FIT=y
 CONFIG_BOOTSTAGE=y
 CONFIG_BOOTSTAGE_REPORT=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/sdb3 init=/sbin/init rootwait ro"
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_CPU_SUPPORT=y