hvmloader, libxl: use the correct ACPI settings depending on device model

hvmloader, libxl: use the correct ACPI settings depending on device model

We need to choose ACPI tables and ACPI IO port location
properly depending on the device model version we are running.
Previously, this decision was made by BIOS type specific
code in hvmloader, e.g. always load QEMU traditional specific
tables if it's ROMBIOS and always load QEMU Xen specific
tables if it's SeaBIOS.

This change saves this behavior (for compatibility) but adds
an additional way (xenstore key) to specify the correct
device model if we happen to run a non-default one. Toolstack
bit makes use of it.

The enforcement of BIOS type depending on QEMU version will
be lifted later when the rest of ROMBIOS compatibility fixes
are in place.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>