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/legoev3_defconfig b/configs/legoev3_defconfig
index 87890cd..d616610 100644
--- a/configs/legoev3_defconfig
+++ b/configs/legoev3_defconfig
@@ -36,6 +36,8 @@
 CONFIG_CMD_DIAG=y
 CONFIG_OF_CONTROL=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="uImage"
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_NET is not set
 CONFIG_DM=y