fdt: Build a U-Boot binary without device tree

At present u-boot.bin holds the plain U-Boot binary without the device tree.
This is somewhat annoying since you need either u-boot.bin or u-boot-dtb.bin
depending on whether device tree is used.

Adjust the build such that u-boot.bin includes a device tree (if enabled),
and the plain binary is in u-boot-nodtb.bin. For now u-boot-dtb.bin remains
the same.

This should be acceptable since:

- without OF_CONTROL, u-boot.bin still does not include a device tree
- with OF_CONTROL, u-boot-dtb.bin does not change

The main impact is build systems which are set up to use u-boot.bin as
the output file and then add a device tree. These will have to change to use
u-boot-nodtb.bin instead.

Adjust tegra rules so it continues to produce the correct files.

Tested-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>