boot/uboot: support binman generated u-boot.itb

When using binman to generate u-boot images, there will no longer be a make
rule for generating files produced by binman.  However, these files will still
need to be installed to the output/images directory.

One such file is the u-boot.itb.  If the u-boot.itb is generated by binman,
then the file still needs to be copied, but without the make rule.

Here is an example of how binman generates the u-boot.itb:
https://source.denx.de/u-boot/u-boot/-/commit/a4c98119109a60b9b236996f47065aa8fc0de9ca

[Tested on Kria KV260 starter kit]
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/uboot/uboot.mk

@@ -103,8 +103,10 @@ endif
 
 ifeq ($(BR2_TARGET_UBOOT_FORMAT_ITB),y)
 UBOOT_BINS += u-boot.itb
+ifneq ($(BR2_TARGET_UBOOT_USE_BINMAN),y)
 UBOOT_MAKE_TARGET += u-boot.itb
 endif
+endif
 
 ifeq ($(BR2_TARGET_UBOOT_FORMAT_IMX),y)
 UBOOT_BINS += u-boot.imx