i965: Enable ARB_texture_gather on Gen7

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

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

@@ -176,6 +176,7 @@ brw_initialize_context_constants(struct brw_context *brw)
       ctx->Const.MaxColorTextureSamples = 8;
       ctx->Const.MaxDepthTextureSamples = 8;
       ctx->Const.MaxIntegerSamples = 8;
+      ctx->Const.MaxProgramTextureGatherComponents = 4;
    }
 
    ctx->Const.MinLineWidth = 1.0;

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

@@ -163,6 +163,10 @@ intelInitExtensions(struct gl_context *ctx)
    if (brw->gen == 5)
       ctx->Extensions.AMD_performance_monitor = true;
 
+   if (brw->gen >= 7) {
+      ctx->Extensions.ARB_texture_gather = true;
+   }
+
    if (ctx->API == API_OPENGL_CORE)
       ctx->Extensions.ARB_base_instance = true;
    if (ctx->API != API_OPENGL_CORE)