Fallback DTB address for virt machine

When using default Aarch64 QEMU ("Tianocore") EFI firmware, the bootloader is able to show display via ramfb device, but unable to boot into the kernel due to Failed to find DTB. This MR provides a quick solution by hardcoding the fallback DTB address until we have a reliable way to detect that this bootloader is loaded via a virt machine.

Reference to hardcoded DTB address

Test result

(Note that the PCID driver is still not working hence unable to use mouse/keyboard)