boot/uboot: add qspi.bin file support

u-boot has introduced a new file called qspi.bin for users who boot from a
qspi flash device.  It combines the spl/boot.bin and u-boot.itb files into a
single binary that can be written to the qspi flash.

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

At the moment, the qspi.bin is only used for the zynqmp platform, but other
platforms may adopt it, so the buildroot support has been made in a generic
way.

This patch adds the necessary support for buildroot to install this binary.

[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/Config.in

@@ -470,6 +470,14 @@ config BR2_TARGET_UBOOT_FORMAT_SD
 
 	  See doc/README.mxs (or doc/README.mx28_common before 2013.07)
 
+config BR2_TARGET_UBOOT_FORMAT_QSPI_BIN
+	bool "qspi.bin"
+	depends on BR2_TARGET_UBOOT_ZYNQMP
+	help
+	  When booting from qspi flash, u-boot can generate a single
+	  file for flashing by combining the spl/boot.bin and
+	  u-boot.itb files into a unified binary.
+
 config BR2_TARGET_UBOOT_FORMAT_STM32
 	bool "u-boot.stm32"
 	depends on BR2_arm

boot/uboot/uboot.mk

@@ -108,6 +108,10 @@ UBOOT_MAKE_TARGET += u-boot.itb
 endif
 endif
 
+ifeq ($(BR2_TARGET_UBOOT_FORMAT_QSPI_BIN),y)
+UBOOT_BINS += qspi.bin
+endif
+
 ifeq ($(BR2_TARGET_UBOOT_FORMAT_IMX),y)
 UBOOT_BINS += u-boot.imx
 UBOOT_MAKE_TARGET += u-boot.imx