Yocto Image will not boot

I asked this question on StackOverflow before but got told here is the right spot to ask. Since im new to Yocto I ran into some problems trying to boot my intel-corei7-64 core-image-minimal from HDD. I used dd to put it on the hard drive but while booting it stops with a Kernel panic:

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown block (0,0)

I tried a lot and searched for a solution. First of all I had to do a grub-install and configured the grub.cfg file in the boot partition to list the Image in GRUB but I am not getting any further than that point. In some forums they said its meaning that the initramfs is missing. I dont think that the image itself is broken because it works on a usb flash drive. My grub.cfg looks like this:

set default="0"
set timeout="30"

menuentry 'Yocto' {
        insmod part_msdos
        insmod part_gpt
        insmod ext2
        insmod all_video
        set root='(hd0,gpt2)'
        linux /boot/bzImage-4.19.40-intel-pk-standard root=/dev/sda2
}

Would be great if you guys could help me fixing the boot error. I am pretty much helpless at this point. Best regards Alex