How to use vendor_boot partition to boot my raspberry pi 4 with AOSP? How to boot using GKI?

Question

I was able to port AOSP on raspberry Pi. I followed this link to achieve the same.

But know what I intent to do is? To boot up my Pi using GKI. Initially I had 4 partitions, Boot, System, vendor and user. I made an additional partition vendor_boot which contains vendor_boot.img, vendor_ramdisk.img and dtb.img. I do not get any logs when I try to boot with this configuration.

    **#Boardconfig.mk**
    BOARD_VENDOR_BOOTIMAGE_PARTITION_SIZE := 103079215104 #96M
    BOARD_INCLUDE_DTB_IN_BOOTIMG := false
    BOARD_BOOT_HEADER_VERSION := 3
    BOARD_MKBOOTIMG_ARGS := --header_version $(BOARD_BOOT_HEADER_VERSION)
    BOARD_USES_VENDOR_BOOTIMAGE := true
    BOARD_USES_GENERIC_KERNEL_IMAGE := true

    **#fstab.rpi**
    /dev/block/mmcblk0p4   /vendor_boot   ext4   ro,barrier=1    wait,first_stage_mount

Above are the following additional configurations I made to accommodate the vendor_boot partition. How will the bootloader know about the vendor_boot partition? Do I need to add any thing more to the vendor_boot partition?