INT 16 - KEYBOARD - GET KEYBOARD FUNCTIONALITY
        AH = 09h
Return: AL = supported keyboard functions (see below)
Note:   this function is only available if bit 6 of the second feature byte
          returned by INT 15/AH=C0h is set
SeeAlso: AH=03h,AH=0Ah,AH=10h,AH=11h,AH=12h,AH=20h,AH=21h,AH=22h,INT 15/AH=C0h

Bitfields for supported keyboard functions:
 bit 7  reserved
 bit 6  INT 16/AH=20h-22h supported (122-key keyboard support)
 bit 5  INT 16/AH=10h-12h supported (enhanced keyboard support)
 bit 4  INT 16/AH=0Ah supported
 bit 3  INT 16/AX=0306h supported
 bit 2  INT 16/AX=0305h supported
 bit 1  INT 16/AX=0304h supported
 bit 0  INT 16/AX=0300h supported

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