OvmfPkg/VmgExitLib: Support string IO for IOIO_PROT NAE events
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
    
    Add support to the #VC exception handler to handle string IO. This
    requires expanding the IO instruction parsing to recognize string based
    IO instructions as well as preparing an un-encrypted buffer to be used
    to transfer (either to or from the guest) the string contents for the IO
    operation. The SW_EXITINFO2 and SW_SCRATCH fields of the GHCB are set
    appropriately for the operation. Multiple VMGEXIT invocations may be
    needed to complete the string IO operation.
    
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
    Acked-by: Laszlo Ersek <lersek@redhat.com>
    Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    Regression-tested-by: Laszlo Ersek <lersek@redhat.com>