i965: Simplify handling of VUE map changes.

i965: Simplify handling of VUE map changes.

The old code was disasterously complex - spread across multiple atoms
which may not even run, inspecting the dirty bits to try and decide
whether it was necessary to do checks...storing VS information in
brw_context...extra flagging...

This code tripped me and Carl up very badly when working on the
shader cache code.  It's very fragile and hard to maintain.

Now that geometry shaders only depend on their inputs and don't have
to worry about the VS VUE map, we can dramatically simplify this:
just compute the VUE map coming out of the geometry shader stage
in brw_upload_programs.  If it changes, flag it.  Done.

v2: Also check vue_map.separable.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>