util: Move ralloc to a new src/util directory.

util: Move ralloc to a new src/util directory.

For a long time, we've wanted a place to put utility code which isn't
directly tied to Mesa or Gallium internals.  This patch creates a new
src/util directory for exactly that purpose, and builds the contents as
libmesautil.la.

ralloc seemed like a good first candidate.  These days, it's directly
used by mesa/main, i965, i915, and r300g, so keeping it in src/glsl
didn't make much sense.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
v2 (Jason Ekstrand): More realloc uses and some scons fixes

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>