I was taking some glances at making this cross-architecture, but the simpler short-term approach is to make this !arm64. Plus for that matter, Xen's EFI/ACPI support on arm64 isn't yet in particularly good shape.

Another alternative would be to have this depend on xentimer, but I've got no idea whether that would be correct (in fact I was under the impression they're quite distinct, so doing that would be an ugly hack).

Ideal solution would be to fix D28619. This though requires merging "bootmethod" from x86 with "arm64_bus_method" from ARM64.

Thing is bootmethod is a string, arm64_bus_method is an enum. The enum seems to make more sense. I'm though curious why the somewhat similar vm_guest variable is declared as an int, even though its values are declared as enums.

Testing confirmed making pvefi.c depend on xentimer works, but I'm unsure whether that is correct.