spearmint: Don't check world surfaces in RE_GetViewFog

It won't work correct and caused RE_GetViewFog to show up fairly high on performence report.
spearmint: Don't sort unused surface sort bytes

Disable some unused sort bytes for better performence.
spearmint: Make DMA active loop sounds a linked list

Increasing the number of entities makes AddLoopSounds and ClearLoopingSounds
slower (~2% execution time vs ioq3 ~0.5%), so use a double linked list of active sounds
(~0.05% execution time).