Revert "intel/compiler: make uses_pos_offset a tri-state"

This reverts commit 5489033fa8.

The problem I was trying to address is that we were programming the
3DSTATE_PS::PositionXYOffsetSelect bit differently with GPL (CENTROID)
than without (NONE).

I failed to understand that this bit also impacts the thread payload
layout. GPL fragment shaders don't know ahead of time if pos_offset is
going to be used. It'll be choosen at runtime base on push constant
bits. So we need to program this bit different just to have a payload
matching the compiled shader code.

This fixes the freedoom replay with GPL FS shader in SIMD32.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Ivan Briano <ivan.briano@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22938>

src/intel/compiler/brw_fs.cpp

@@ -7365,16 +7365,12 @@ brw_nir_populate_wm_prog_data(const nir_shader *shader,
        * per-sample dispatch.  If we need gl_SamplePosition and we don't have
        * persample dispatch, we hard-code it to 0.5.
        */
-      prog_data->read_pos_offset_input =
-         BITSET_TEST(shader->info.system_values_read,
-                     SYSTEM_VALUE_SAMPLE_POS) ||
-         BITSET_TEST(shader->info.system_values_read,
-                     SYSTEM_VALUE_SAMPLE_POS_OR_CENTER);
-
-      if (prog_data->read_pos_offset_input)
-         prog_data->uses_pos_offset = prog_data->persample_dispatch;
-      else
-         prog_data->uses_pos_offset = BRW_NEVER;
+      prog_data->uses_pos_offset =
+         prog_data->persample_dispatch != BRW_NEVER &&
+         (BITSET_TEST(shader->info.system_values_read,
+                      SYSTEM_VALUE_SAMPLE_POS) ||
+          BITSET_TEST(shader->info.system_values_read,
+                      SYSTEM_VALUE_SAMPLE_POS_OR_CENTER));
    }
 
    prog_data->has_render_target_reads = shader->info.outputs_read != 0ull;