Dos 4+ XMA2EMS.SYS extension internal - Get hidden frame info

        Entry:
          AX = 1B01h
          DI = hidden physical page number
        Return:
          AX = FFFFh if failed (no such hidden page)
          AX = 0000h if OK, then
               ES = segment of page frame
               DI = physical page number

        Note: This corresponds to the data edited out of the
              INT 67 AH=58h call