OvmfPkg/AcpiPlatformDxe/QemuLoader.h: remove QemuFwCfgLib class dependency

OvmfPkg/AcpiPlatformDxe/QemuLoader.h: remove QemuFwCfgLib class dependency

"QemuLoader.h" needs the QEMU_FW_CFG_FNAME_SIZE macro. This macro used to
live in the QemuFwCfgLib class header, but we moved it to the more
foundational IndustryStandard include file called "QemuFwCfg.h" in commit
5583a8a4ffd0 ("OvmfPkg/QemuFwCfgLib: move types/macros from lib class to
IndustryStandard", 2017-02-22).

Replace the lib class dependency with the more basic IndustryStandard
dependency in "QemuLoader.h".

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2122
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210526201446.12554-9-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>