anv: add support for extended texture gather

Now that the SPIR-V -> NIR translation is in place, no additional logic
is required.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Acked-by: Jason Ekstrand <jason.ekstrand@intel.com>

src/intel/vulkan/TODO

@@ -4,7 +4,6 @@ Intel Vulkan ToDo
 Missing Features:
  - FP64
  - Tessellation
- - Image Gather Extended
  - Storage Image Without Format
  - Investigate CTS failures on HSW
  - Pipeline statistics queries

src/intel/vulkan/anv_device.c

@@ -468,7 +468,7 @@ void anv_GetPhysicalDeviceFeatures(
       .pipelineStatisticsQuery                  = false,
       .fragmentStoresAndAtomics                 = true,
       .shaderTessellationAndGeometryPointSize   = true,
-      .shaderImageGatherExtended                = false,
+      .shaderImageGatherExtended                = true,
       .shaderStorageImageExtendedFormats        = true,
       .shaderStorageImageMultisample            = false,
       .shaderStorageImageReadWithoutFormat      = false,