i965: Split VUE map handling out of brw_vs.c into brw_vue_map.c.

i965: Split VUE map handling out of brw_vs.c into brw_vue_map.c.

This was originally only used by the vertex shader, but it's now used by
the geometry shader as well, and will also eventually be used for
tessellation control and evaluation shaders.

I suspect it will be easier to find in a file named after the concept.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>