Re-add ACPI SPCR (serial console) support
    
    Four SPCR patches were merged upstream into 4.9, but one was reverted by a
    subsequent commit (due to a trivial merge conflict with a later, unrelated
    patch). A fixed up version of the missing patch is queued up for 4.10 in
    tty-next. Carry it to make sure users see serial console output on ACPI
    systems. Otherwise manually setting console=ttyAMAn would be required.