Is there a possibility to add another targets for buildroot to make, apart from rootfs, Linux kernel image, and Uboot? In my use case I want to build boot image for Zynq, which consists of FSBL, bitstream for FPGA part of Zynq, Uboot, Linux kernel, device tree, and rootfs. There is no automatic way to make FSBL and bitstream (I know about Uboot SPL, but I can't use it, because I need my custom FSBL). Can I somehow add this targets for Buildroot, so that it builds this two targets, and copy artifacts to output/images? Then I would be able to use it in post image script, to create final image (BOOT.bin, or BOOT.mcs).
You can add two new packages (let's say fsbl and bitstream), and each of them can install in output/images. Every package creates a make target equal to the package name, so you would have make fsbl and make bitstream.
Have a look at the manual for instructions on how to add packages.