added a test case to directly compare im2col and implicit gemm

Author: bssrdf

tests/CMakeLists.txt

@@ -198,6 +198,7 @@ if (NOT LLAMA_SANITIZE_ADDRESS)
 endif()
 llama_build_and_test(test-gguf.cpp)
 llama_build_and_test(test-backend-ops.cpp)
+llama_build_and_test(test-conv2d.cpp)
 
 llama_build_and_test(test-model-load-cancel.cpp  LABEL "model")
 llama_build_and_test(test-autorelease.cpp        LABEL "model")