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/microblaze-generic_defconfig b/configs/microblaze-generic_defconfig
index 492be51..a3729fb 100644
--- a/configs/microblaze-generic_defconfig
+++ b/configs/microblaze-generic_defconfig
@@ -12,6 +12,8 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_BOOTDELAY=-1
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=romfs"
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SPL=y
 CONFIG_SPL_BOARD_INIT=y