i965: Enable ARB_texture_gather for one component on Gen6.

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

src/mesa/drivers/dri/i965/brw_context.c

@@ -374,6 +374,8 @@ brw_initialize_context_constants(struct brw_context *brw)
 
    if (brw->gen >= 7)
       ctx->Const.MaxProgramTextureGatherComponents = 4;
+   else if (brw->gen == 6)
+      ctx->Const.MaxProgramTextureGatherComponents = 1;
 
    ctx->Const.MinLineWidth = 1.0;
    ctx->Const.MinLineWidthAA = 1.0;

src/mesa/drivers/dri/i965/intel_extensions.c

@@ -270,6 +270,7 @@ intelInitExtensions(struct gl_context *ctx)
       ctx->Extensions.ARB_texture_multisample = true;
       ctx->Extensions.ARB_sample_shading = true;
       ctx->Extensions.ARB_vertex_type_10f_11f_11f_rev = true;
+      ctx->Extensions.ARB_texture_gather = true;
 
       /* Test if the kernel has the ioctl. */
       if (drm_intel_reg_read(brw->bufmgr, TIMESTAMP, &dummy) == 0)
@@ -284,7 +285,6 @@ intelInitExtensions(struct gl_context *ctx)
    }
 
    if (brw->gen >= 7) {
-      ctx->Extensions.ARB_texture_gather = true;
       ctx->Extensions.ARB_conservative_depth = true;
       ctx->Extensions.AMD_vertex_shader_layer = true;
       if (can_do_pipelined_register_writes(brw)) {