We currently use the EFI_CPU_ARCH_PROTOCOL's GetTimerValue() method to
generate the currticks() timer, calibrated against a 1ms delay from
the boot services Stall() method.
This does not work on ARM platforms, where GetTimerValue() is an empty
stub which just returns EFI_UNSUPPORTED.
Fix by instead creating a periodic timer event, and using this event
to increment a current tick counter.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
757ab98381