Convert CONFIG_BOOTFILE to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTFILE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/uniphier_v8_defconfig b/configs/uniphier_v8_defconfig
index b9e2d9b..8269aab 100644
--- a/configs/uniphier_v8_defconfig
+++ b/configs/uniphier_v8_defconfig
@@ -34,6 +34,8 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=uniphier-nand.0:1m(firmware),-(UBI)"
 CONFIG_CMD_UBI=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="Image"
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_GPIO_UNIPHIER=y
 CONFIG_MISC=y