Select display page

        Entry:
          AH = 05h
          AL =
              0-7: new page value for modes 0 & 1
              0-3: new page value for modes 2 & 3
              {Corona/Cordata BIOS v4.10+}
              0: set address of graphics bitmap buffer (video modes 60h,61h)
                  BX = segment of buffer
              0Fh: get address of graphics bitmap buffer (video modes 60h,61h)
        Return:
          BH = CRT page register (if AL >= 80h)
          BL = CPU page register (if AL >= 80h)
          DX = segment of graphics bitmap buffer (video modes 60h,61h; AL=0Fh)
          AX,SI,DI,BP destroyed by call