Expects: AX    001eH
Returns: BX    video page upon which the mouse is displayed
Info: This returns the video page number upon which the mouse support
is currently displaying the mouse pointer.

This does not tell you which video page is currently active.  Use
INT 10H 0fH to learn that.  Use INT 10H 05H to activate a
particular video page.

- -

INT 33H 001eH: Query Mouse Display Page