OvmfPkg/PciHostBridgeLibScan: create from PciHostBridgeLib

OvmfPkg/PciHostBridgeLibScan: create from PciHostBridgeLib

Create an almost verbatim copy of the
"OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.inf" library instance.

The new PciHostBridgeLibScan instance will ultimately duplicate a
negligible amount of code from the original, and will be used by the Bhyve
and OvmfXen platforms.

List the new driver in "Maintainers.txt", in the "OvmfPkg: bhyve-related
modules" and "OvmfPkg: Xen-related modules" sections.

This patch should be reviewed with "git show --find-copies-harder".

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Cc: Peter Grehan <grehan@freebsd.org>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Rebecca Cran <rebecca@bsdio.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2122
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210526201446.12554-30-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>