INT 31 P - DPMI 1.0+ - ALLOCATE LINEAR MEMORY BLOCK
        AX = 0504h
        EBX = page-aligned linear address of memory block (00000000h if any
                address is acceptable)
        ECX = size in bytes (nonzero)
        EDX = flags
            bit 0: set to create committed pages instead of uncommitted pages
            bits 1-31: reserved (0)
Return: CF clear if successful
            EBX = linear address of memory block
            ESI = memory block handle
        CF set on error
            AX = error code (8001h,8012h-8014h,8016h,8021h,8025h)(see AX=0000h)
Note:   only supported by 32-bit DPMI hosts, but may be used by 16-bit clients
SeeAlso: AX=0505h