INT 21 - Phar Lap 386/DOS-Extender VMM - LOCK PAGES IN MEMORY
        AX = 251Ah
        EDX = number of 4k pages to lock
        if BL = 00h
            ECX = linear address of first page to lock
        if BL = 01h
            ES:ECX -> pointer to first page to lock
Return: CF clear if successful
        CF set on error
            EAX = error code
                08h insufficient memory
                09h invalid address range
SeeAlso: AX=EB06h,INT 31/AX=0600h