Convert CONFIG_LAST_STAGE_INIT to Kconfig

This converts the following to Kconfig:
   CONFIG_LAST_STAGE_INIT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/cortina_presidio-asic-emmc_defconfig b/configs/cortina_presidio-asic-emmc_defconfig
index 9d5921a..a96e251 100644
--- a/configs/cortina_presidio-asic-emmc_defconfig
+++ b/configs/cortina_presidio-asic-emmc_defconfig
@@ -12,6 +12,7 @@
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_BOOTDELAY=3
 CONFIG_BOARD_EARLY_INIT_R=y
+CONFIG_LAST_STAGE_INIT=y
 CONFIG_SYS_PROMPT="G3#"
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y