OvmfPkg/VirtioFsDxe: add a shared wrapper for FUSE_FSYNC / FUSE_FSYNCDIR

OvmfPkg/VirtioFsDxe: add a shared wrapper for FUSE_FSYNC / FUSE_FSYNCDIR

The FUSE_FSYNC and FUSE_FSYNCDIR commands only differ in the opcode. Add a
common function for wrapping both.

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3097
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201216211125.19496-14-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>