PCI/ACPI: Run _OSC only once for OSPM feature support

Previously, we ran _OSC once to tell the platform that we support
PCI Segment Groups, then we ran it again if we supported any additional
features (ASPM, MSI, or extended config space).  I don't think it's
necessary to run it twice, since we can easily build the complete
mask of features we support before running _OSC the first time.

We run _OSC again later when requesting control of PCIe features;
that's unaffected by this change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>