Add chw 3x3s2p1_scalar kernels.

PiperOrigin-RevId: 275004948
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3b483af..2cb377c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -175,6 +175,7 @@
   src/f32-dwconv/up1x4-scalar.c
   src/f32-dwconv/up1x9-scalar.c
   src/f32-dwconv-spchw/3x3p1-scalar.c
+  src/f32-dwconv-spchw/3x3s2p1-scalar.c
   src/f32-gavgpool/mp7p7q-scalar.c
   src/f32-gavgpool/up7-scalar.c
   src/f32-gemm/1x4-scalar.c