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/socfpga_dbm_soc1_defconfig b/configs/socfpga_dbm_soc1_defconfig
index 15652a1..24687f1 100644
--- a/configs/socfpga_dbm_soc1_defconfig
+++ b/configs/socfpga_dbm_soc1_defconfig
@@ -46,6 +46,8 @@
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="fitImage"
 CONFIG_VERSION_VARIABLE=y
 CONFIG_DFU_MMC=y
 CONFIG_SYS_DFU_DATA_BUF_SIZE=0x1000000