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/integratorcp_cm920t_defconfig b/configs/integratorcp_cm920t_defconfig
index 06bfdff..ddff8ac 100644
--- a/configs/integratorcp_cm920t_defconfig
+++ b/configs/integratorcp_cm920t_defconfig
@@ -23,6 +23,8 @@
 CONFIG_CMD_ARMFLASH=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_ENV_ADDR=0x24F00000
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="uImage"
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_FLASH_CFI_DRIVER=y