!UPSTREAM: i965/vec4: Allow MOV from vec4 or vec8 into vec4.

This can only happen when doing attribute fixup for
DUAL_INSTANCED geometry shaders.

TODO:
- Add force_writemask_all to "swizzle gl_PointSize input"
- Better commit message
- Better comment at the site of the MOV fixup
!UPSTREAM: Fixes to vertex reordering workaround

TODO:
- Fold into vertex reordering code.
!UPSTREAM: i965/vec4: fix up primitive ID workaround for DUAL_INSTANCE dispatch.

TODO:

- Add better explanatory comments in generate_vec4_instruction.

- Modify the patch that does similar things to
  generate_vec4_instruction's MOV case and add better explanatory
  comments to it too.