INT 62 u - FGDRIVER v4.02 - "FG_WAITVR" - ENABLE/DISABLE VERTICAL RETRACE WAIT
	AX = 00DFh
	BX = new state (0000h disabled, 0001h enabled)
Note:	the FGDRIVER functions are rearranged with each major release, but
	  their parameters do not change (see #03474 at AX=0000h)