ArmVirtPkg/QemuFwCfgLib: allow UEFI_DRIVER modules

We don't distribute UEFI_DRIVER modules stand-alone that were built as
part of an ArmVirtQemu* platform. ArmVirtQemu* UEFI_DRIVERs are allowed to
inherit platform dependencies.

By enabling UEFI_DRIVERs to consume QemuFwCfgLib, we can hook fw_cfg-based
NULL class libraries into UEFI drivers, e.g. in order to set dynamic PCDs.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Per Sundstrom <per_sundstrom@yahoo.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2681
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200424075353.8489-7-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

ArmVirtPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf

@@ -15,7 +15,7 @@
   FILE_GUID                      = B271F41F-B841-48A9-BA8D-545B4BC2E2BF
   MODULE_TYPE                    = BASE
   VERSION_STRING                 = 1.0
-  LIBRARY_CLASS                  = QemuFwCfgLib|DXE_DRIVER
+  LIBRARY_CLASS                  = QemuFwCfgLib|DXE_DRIVER UEFI_DRIVER
 
   CONSTRUCTOR                    = QemuFwCfgInitialize