Expects: AX    4f03H
Returns: AX    VESA status: AH=0 means successful (else failed)
AL=4fH means function supported
BX    VESA/SVGA Video Mode number currently active
Info: Obtains the number of the current video mode.

Notes:   Unlike INT 10H 0fH, this does NOT return the state of "clear
video memory bit" that was used when the mode was initialized;
that is, only the high bit of BX always comes back as 0.

See Also: SVGA
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INT 10H 4f03H - Query Current SuperVGA Video Mode