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/cougarcanyon2_defconfig b/configs/cougarcanyon2_defconfig
index 073807b..9dd1082 100644
--- a/configs/cougarcanyon2_defconfig
+++ b/configs/cougarcanyon2_defconfig
@@ -41,6 +41,8 @@
 CONFIG_EFI_PARTITION=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_BOOTFILE=y
+CONFIG_BOOTFILE="bzImage"
 CONFIG_TFTP_TSIZE=y
 CONFIG_REGMAP=y
 CONFIG_SYSCON=y