Fix some additional bugs, OSDSYS now loading!

* Fixed bug when writing to DICR/DICR2 flag field
* Fixed definition of the DMAC tag
* SIF0 doesn't use the id field, apparently?
* Allow writing to some specific regions of the BIOS

With these changes OSDSYS has now started loading! The BIOS
is initiallizing the SPU2, probably to play that boot up charm
the PS2 does.