dma/rc4030: translate memory accesses only when they occur

This simplifies the code a lot, and this fixes big memory leaks
introduced in a3d586f7

Windows NT is now able to boot without using gigabytes of ram on the host.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Reviewed-by: Yongbok Kim <yongbok.kim@imgtec.com>
Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com>