PCI: acpi_pcihp: run _OSC on a root bridge

_OSC should be ran on a root bridge instead of the device itself.  Do
this before touching OSHP since PCI fw specs states that _OSC should be
preferred over OSHP (however if the device has OSHP but not _OSC -- not
a root bridge -- it's not).

Cc: kristen.c.accardi@intel.com
Acked-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>