MinPlatformPkg: Add multiple segment support for PciHostBridgeLib

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1799



1. Add PcdPciSegmentCount PCD in MinPlatformPkg.dec and set default to 1
2. Base on PciHostBridge related PCDs to Initialize RootBridges.

Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marc Chen <marc.w.chen@intel.com>
Reviewed-by: Rangasai V Chaganty <rangasai.v.chaganty@intel.com>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>