OvmfPkg/AcpiPlatformDxe: move "QemuLoader.h" to IndustryStandard

OvmfPkg/AcpiPlatformDxe: move "QemuLoader.h" to IndustryStandard

Turn the "QemuLoader.h" header into a public (IndustryStandard) one. The
QEMU ACPI linker-loader interface is stable between QEMU and multiple
guest firmwares.

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: <20210526201446.12554-10-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>