INT 6F - HP Vectra EX-BIOS - "F_IO_CTRL SF_LOCK" - RESERVE SUB-ADDRESSES
	AX = 0400h
	BP = driver ID (see #03741)
	DH,DL = major,minor address (optional)
Return: AH = status (see #03744)
	BP,DS destroyed
Desc:	reserve specified sub-addresses on an already-allocated driver for
	  exclusive access
Note:	this function is documented as present but unsupported in the drivers
	  V_LTABLET, V_LPOINTER, and V_LTOUCH
SeeAlso: AX=0200h"HP Vectra",AX=0402h"SF_UNLOCK"