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/efi-x86_app32_defconfig b/configs/efi-x86_app32_defconfig
index bb4c405..228643a 100644
--- a/configs/efi-x86_app32_defconfig
+++ b/configs/efi-x86_app32_defconfig
@@ -32,6 +32,8 @@
 CONFIG_OF_EMBED=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="bzImage"
 CONFIG_REGMAP=y
 CONFIG_SYSCON=y
 # CONFIG_REGEX is not set