PCI: Add has_mem64 for struct host_bridge

PCI: Add has_mem64 for struct host_bridge

Add has_mem64 for struct host_bridge, on root bus that does not support
mmio64 above 4g, will not set that.

We will use that info next two following patches:
1. Don't treat non-pref mmio64 as pref mmio, so will not put
   it under bridge's pref range when rescan the devices
2. will keep pref mmio64 and pref mmio32 under bridge pref bar.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Orabug: 21826746

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
(cherry picked from commit a60c5ffaf17466433caac32fea9c45576ecdf5c4)