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/work_92105_defconfig b/configs/work_92105_defconfig
index 8b21dc2..c702491 100644
--- a/configs/work_92105_defconfig
+++ b/configs/work_92105_defconfig
@@ -45,6 +45,8 @@
 CONFIG_DOS_PARTITION=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="uImage"
 CONFIG_VERSION_VARIABLE=y
 CONFIG_LPC32XX_GPIO=y
 CONFIG_SYS_I2C_LEGACY=y