acpi: serial: don't use _STA method

acpi: serial: don't use _STA method

The _STA method dates back to the days where we had a static DSDT.  The
device is listed in the DSDT table unconditionally and the _STA method
checks a bit in the isa bridge pci config space to figure whenever a
given is isa device is present or not, then evaluates to 0x0f (present)
or 0x00 (absent).

These days the DSDT is generated by qemu anyway, so if a device is not
present we can simply drop it from the DSDT instead.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200515150421.25479-5-kraxel@redhat.com>