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/theadorable-x86-conga-qa3-e3845_defconfig b/configs/theadorable-x86-conga-qa3-e3845_defconfig
index f9ac967..9d2f5b9 100644
--- a/configs/theadorable-x86-conga-qa3-e3845_defconfig
+++ b/configs/theadorable-x86-conga-qa3-e3845_defconfig
@@ -17,6 +17,7 @@
 CONFIG_BOOTSTAGE=y
 CONFIG_BOOTSTAGE_REPORT=y
 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