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>