st/mesa: set MaxUnrollIterations = 255

The default was 32 for the EmitNoLoops=0 case.  This allows the oZone3D
soft shadows test to work properly with the vmware driver.  Jose reported
that SM3 supports up to 255 loop iterations.

NOTE: This is a candidate for the 8.0 branch.

Reviewed-by: José Fonseca <jfonseca@vmware.com>
1 file changed