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/edb9315a_defconfig b/configs/edb9315a_defconfig
index adc9a68..e723792 100644
--- a/configs/edb9315a_defconfig
+++ b/configs/edb9315a_defconfig
@@ -2,6 +2,8 @@
 CONFIG_TARGET_EDB93XX=y
 CONFIG_SYS_EXTRA_OPTIONS="MK_edb9315a"
 CONFIG_ENV_IS_IN_FLASH=y
+CONFIG_USE_BOOTARGS=y
+CONFIG_BOOTARGS="root=/dev/nfs console=ttyAM0,115200 ip=dhcp"
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_BOARD_EARLY_INIT_F=y