mesa: Default to GL 3.1's limits on uniform blocks.

mesa: Default to GL 3.1's limits on uniform blocks.

The ARB spec lets you get away with the default block counting against the
blocks for combined size limits.  The core spec says you need to be able to
support the maximum size of default block *and* the maximum size of each
uniform block.  I see no reason that any driver would have a problem with
that.

Fixes gl 3.1/minmax (with an associated fix to the test)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>