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/crownbay_defconfig b/configs/crownbay_defconfig
index 00df2f6..4e4f471 100644
--- a/configs/crownbay_defconfig
+++ b/configs/crownbay_defconfig
@@ -12,6 +12,7 @@
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/sdb3 init=/sbin/init rootwait ro"
 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