pc: set the OEM fields in the RSDT and the FADT from the SLIC

The Microsoft spec about the SLIC and MSDM ACPI tables at
<http://go.microsoft.com/fwlink/p/?LinkId=234834> requires the OEM ID and
OEM Table ID fields to be consistent between the SLIC and the RSDT/XSDT.
That further affects the FADT, because a similar match between the FADT
and the RSDT/XSDT is required by the ACPI spec in general.

This patch wires up the previous three patches.

Cc: "Michael S. Tsirkin" <mst@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Igor Mammedov <imammedo@redhat.com> (supporter:ACPI/SMBIOS)
Cc: Paolo Bonzini <pbonzini@redhat.com> (maintainer:X86)
Cc: Richard W.M. Jones <rjones@redhat.com>
Cc: Aleksei Kovura <alex3kov@zoho.com>
Cc: Michael Tokarev <mjt@tls.msk.ru>
Cc: Steven Newbury <steve@snewbury.org.uk>
RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1248758
LP: https://bugs.launchpad.net/qemu/+bug/1533848
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Steven Newbury <steve@snewbury.org.uk>
