Expects: AX    0021H
                                                                  
Returns: AX    status: 0021H=success
ffffH=can't reset (no driver)
BX    number of mouse buttons
                                                                  
Info: This performs a "software reset" of the mouse support.  It sets
all internal variables to their standard defaults, as described

This works like INT 33H 0000H except that it does not perform a
reset of the mouse hardware or of any hardware-related variables
(some older mouse hardware takes several seconds to reset).

- -

INT 33H 0021H: Reset Mouse Driver