gallium: add a cap for supporting 4-offset TG4 opcodes

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
diff --git a/src/gallium/drivers/i915/i915_screen.c b/src/gallium/drivers/i915/i915_screen.c
index 8ee4330..dfd7a2e 100644
--- a/src/gallium/drivers/i915/i915_screen.c
+++ b/src/gallium/drivers/i915/i915_screen.c
@@ -221,6 +221,7 @@
    case PIPE_CAP_FAKE_SW_MSAA:
    case PIPE_CAP_TEXTURE_QUERY_LOD:
    case PIPE_CAP_SAMPLE_SHADING:
+   case PIPE_CAP_TEXTURE_GATHER_OFFSETS:
       return 0;
 
    case PIPE_CAP_MAX_DUAL_SOURCE_RENDER_TARGETS: