Hello Ard,
KvmTool, Qemu, Xen and CloudHv use the following implementation:
PlatformBootManagerLib|ArmPkg/Library/PlatformBootManagerLib/PlatformBootManagerLib.inf

Testing:
- using kvmtool
- not pressing any key during the process
I end-up in the boot menu (so not the UEFI shell).

When trying with a zero-ed flash.img, kvmtool exits with the following:
'PlatformBootManagerUnableToBoot: rebooting after refreshing all boot options'
Then the flash is populated and the second attempt reaches the boot menu.

With the new PcdUefiShellDefaultBootEnable set to TRUE, we directly reach
the UEFI shell.

Regards,
Pierre