treewide: Migrate CONFIG_LAST_STAGE_INIT to Kconfig

Migrate the CONFIG_LAST_STAGE_INIT option to Kconfig.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/configs/dfi-bt700-q7x-151_defconfig b/configs/dfi-bt700-q7x-151_defconfig
index fa6ccc4..94cc5ec 100644
--- a/configs/dfi-bt700-q7x-151_defconfig
+++ b/configs/dfi-bt700-q7x-151_defconfig
@@ -17,6 +17,7 @@
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/sda1 ro quiet"
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
+CONFIG_LAST_STAGE_INIT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_CPU=y
 # CONFIG_CMD_FLASH is not set