intel/fs/gen12: Fix Render Target Read header setup for new thread payload layout.

intel/fs/gen12: Fix Render Target Read header setup for new thread payload layout.

In Gen12 the Poly 0 Info DWORD containing the Viewport Index and
Render Target Index fields were moved from r0.0 to r1.1 in order to
make room for dual-polygon dispatch.  The render target message format
was updated to expect that information in the same location, so we
didn't need to make any changes for framebuffer fetch to work with
SIMD8 and SIMD16 dispatch.  Unfortunately that won't work with SIMD32,
since the render target message header is assembled from r0 and r2
instead of r1, and the r2 thread payload wasn't updated with an
additional copy of the same information.  We need to fix things up
manually instead.  This avoids a handful of
EXT_shader_framebuffer_fetch regressions in combination with SIMD32
fragment shaders.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>