spearmint: Fix restoring overridden latch cvars defaults
spearmint: Extend fogParms, remove linearFogParms

ET changed fogParms from exp fog to linear fog. I originally added
linearFogParms and create patch shaders for ET. There is a few issues
with this.

q3map2 will only create fog volume if fogParms is in shader, so for new
maps you would need to specify fogParms and linearFogParms.
By requiring ET maps to have patch data to use linear fog there would be
issues with add on maps.

Allow fog type to be specified at end of fogParms and fall back to type
set by r_defaultFogParmsType (which can be set by gameconfig.txt).

Fixes q3map2 issue and ET can have fogParms default to linear.