Mipmapping and other texture filters now work.

Mipmapping and other texture filters now work.
Beaware that R300_TX_MIN_FILTER_MASK might be incorrect because i havent
been able to confirm that all filters operate correctly. Because of this its
also pretty pointless trying to get other features that use filter field to
work.

Lod bias should also work but have been unable to test it because lodbias
test doesnt work.