Update on "[ET-VK][ez] Misc fixes related to extension support checking"

## Context

Follow up from #7576. Apply two "fixes" that were missed in the first diff:

1. Check device capability for Prepacking nodes as well
2. Remove conditional skips during generated operator correctness tests; rely on the device capability check to determine if a skip is needed.

Differential Revision: [D68035430](https://our.internmc.facebook.com/intern/diff/D68035430/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/test/op_tests/utils/gen_computegraph.py

@@ -633,6 +633,30 @@ def gen_graph_exec_code(self, check_output=True) -> str:
 
         return graph_exec
 
+    def gen_conditional_skips(self, skip_str: str = "GTEST_SKIP();") -> str:
+        fp16_skip = f"if (!{self.graph}{self.dot}context()->adapter_ptr()->has_full_float16_buffers_support()) {{\n"
+        fp16_skip += f"  {skip_str}\n"
+        fp16_skip += "}"
+        fp16_skip = re.sub(r"^", "  ", fp16_skip, flags=re.M) + "\n"
+
+        int8_skip = f"if (!{self.graph}{self.dot}context()->adapter_ptr()->has_full_int8_buffers_support()) {{\n"
+        int8_skip += f"  {skip_str};\n"
+        int8_skip += "}\n"
+
+        skips = ""
+
+        skips += "if (test_dtype == at::kHalf) {\n"
+        skips += fp16_skip
+        skips += "}\n"
+
+        for _, dtype in self.suite_def.arg_dtype.items():
+            if dtype == "at::kChar" or dtype == "at::kQInt8":
+                skips += int8_skip
+                continue
+
+        skips += "\n"
+        return skips
+
     def gen_op_check_fn(self) -> str:
         op_name = self.f.func.name.unambiguous_name()
         if self.suite_def.test_name_suffix is not None: