AmpereSiliconPkg: Add PlatformManagerUiLib library instance

The idea came from DeviceManagerUiLib that all related menu settings can
be placed under a common entry. This change intends to provide a central
point for all platform menus by creating a Platform Manager entry located
under Device Manager entry of UiApp.

New classuuid called gPlatformManagerFormsetGuid was introduced for
platform menus which want to be reached through this Platform Manager.

Cc: Thang Nguyen <thang@os.amperecomputing.com>
Cc: Chuong Tran <chuong@os.amperecomputing.com>
Cc: Phong Vo <phong@os.amperecomputing.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>

Signed-off-by: Nhi Pham <nhi@os.amperecomputing.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>