conf/board: newer kernels must use mainline aft

newer kernels with cpuidle fix can't use older atf
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>

conf/board

@@ -79,11 +79,11 @@ case ${pureos_board} in
         ;;
       next)
         kernel_url="${kernel_base}/kernel_devkit_linux-next_imx8-linux-next-devkit/${archive_path}"
-        uboot_url="${uboot_base}/uboot_devkit_build/${archive_path}"
+        uboot_url="${uboot_base}/uboot_devkit_mainline_atf_build/${archive_path}"
 	;;
       current)
         kernel_url="${kernel_base}/kernel_devkit_linux-next_imx8-5.2-devkit/${archive_path}"
-        uboot_url="${uboot_base}/uboot_devkit_build/${archive_path}"
+        uboot_url="${uboot_base}/uboot_devkit_mainline_atf_build/${archive_path}"
         ;;
       *)
 	echo "unknown kernel type for devkit build ${build_type}"