[ET-VK] Tuning local workgroup size calculation for conv2d pw to improve performance.

This diff adjusts the local workgroup size (`local_wg_size`) based on batch count (stored in  `wg_size[1]`), to improve conv2d pw performance.

* If `wg_size[1]` is a multiple of 8, `local_wg_size_y` is set to 8.
* If `wg_size[1]` is a multiple of 4, `local_wg_size_y` is set to 4.
* If `wg_size[1]` is a multiple of 2, `local_wg_size_y` is set to 2.
* Otherwise, we default to `local_wg_size_y` = 1.

The dispatch size in 2 dimensions is then calculate based on `{64 / local_wg_size_y, local_wg_size_y, 1}`.

Differential Revision: [D75420517](https://our.internmc.facebook.com/intern/diff/D75420517/)

[ghstack-poisoned]

Author: trivedivivek

backends/vulkan/runtime/graph/ops/impl/Convolution.cpp

@@ -404,6 +404,21 @@ void add_conv2d_node(
     wg_size = {wg_size[0] * wg_size[1], wg_size[2], 1};
   }
 
+  utils::uvec3 local_wg_size;
+  if (method == Conv2dMethod::Pointwise) {
+    uint32_t local_wg_size_y = 1;
+    if (wg_size[1] % 8 == 0) {
+      local_wg_size_y = 8;
+    } else if (wg_size[1] % 4 == 0) {
+      local_wg_size_y = 4;
+    } else if (wg_size[1] % 2 == 0) {
+      local_wg_size_y = 2;
+    }
+    local_wg_size = {64 / local_wg_size_y, local_wg_size_y, 1};
+  } else {
+    local_wg_size = graph.create_local_wg_size(wg_size);
+  }
+
   vkapi::ParamsBindList param_buffers;
   std::vector<PushConstantDataInfo> push_constants;
   if (method == Conv2dMethod::Pointwise) {
@@ -464,7 +479,7 @@ void add_conv2d_node(
       graph,
       shader,
       wg_size,
-      graph.create_local_wg_size(wg_size),
+      local_wg_size,
       // Inputs and Outputs
       {{out, vkapi::kWrite}, {{in, arg_weight, arg_bias}, vkapi::kRead}},
       // Shader params buffers