loader.efi: detect console from ConsOut
UEFI systems should set ConOut and ConOutDev variables with device paths of console devices. Try to identify console devices from it. The goal is to get better approach then just attempting to activate all possible variants. There are some issues, however.
ConOut/ConOutDev variables may not be present (rare, but have reports of such systems). In such case, we default to video console, because it is more common to have video console than serial (except on servers, perhaps).
Serial device identification will need more work (walking acpi tables and such), at this time, we are just noting the serial is there, and we are concentrating on parsing and walking device paths.
Patch adopted from FreeBSD.