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/T2080QDS_SPIFLASH_defconfig b/configs/T2080QDS_SPIFLASH_defconfig
index 8fd0248..78d859a 100644
--- a/configs/T2080QDS_SPIFLASH_defconfig
+++ b/configs/T2080QDS_SPIFLASH_defconfig
@@ -56,6 +56,8 @@
 CONFIG_OF_CONTROL=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="uImage"
 CONFIG_DM=y
 CONFIG_SYS_SATA_MAX_DEVICE=2
 CONFIG_FSL_CAAM=y