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/hsdk_defconfig b/configs/hsdk_defconfig
index c72ad9f..cd9f697 100644
--- a/configs/hsdk_defconfig
+++ b/configs/hsdk_defconfig
@@ -35,6 +35,8 @@
 CONFIG_ENV_IS_IN_FAT=y
 CONFIG_ENV_FAT_DEVICE_AND_PART="0:1"
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="uImage"
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_CLK_HSDK=y
 CONFIG_HSDK_CREG_GPIO=y