i965/gen7_urb: Re-emit PUSH_CONSTANT_ALLOC on some gen9

i965/gen7_urb: Re-emit PUSH_CONSTANT_ALLOC on some gen9

According to internal docs, some gen9 platforms have a pixel shader push
constant synchronization issue. Although not listed among said
platforms, this issue seems to be present on the GeminiLake 2x6's we've
tested.

We consider the available workarounds to be too detrimental on
performance. Instead, we mitigate the issue by applying part of one of
the workarounds. Re-emit PUSH_CONSTANT_ALLOC at the top of every batch
(as suggested by Ken).

Fixes ext_framebuffer_multisample-accuracy piglit test failures with the
following options:
* 6 depth_draw small depthstencil
* 8 stencil_draw small depthstencil
* 6 stencil_draw small depthstencil
* 8 depth_resolve small
* 6 stencil_resolve small depthstencil
* 4 stencil_draw small depthstencil
* 16 stencil_draw small depthstencil
* 16 depth_draw small depthstencil
* 2 stencil_resolve small depthstencil
* 6 stencil_draw small
* all_samples stencil_draw small
* 2 depth_draw small depthstencil
* all_samples depth_draw small depthstencil
* all_samples stencil_resolve small
* 4 depth_draw small depthstencil
* all_samples depth_draw small
* all_samples stencil_draw small depthstencil
* 4 stencil_resolve small depthstencil
* 4 depth_resolve small depthstencil
* all_samples stencil_resolve small depthstencil

v2: Include more platforms in WA (Ken).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106865
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93355
Cc: <mesa-stable@lists.freedesktop.org>
Tested-by: Mark Janes <mark.a.janes@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>