[Silabs] Fix enable_openthread_cli/uart build configuration (#25835)

* This fix an issue where openthread cli was defined and uart files compiled when if not needed mostly on the wifi builds

* The conditional default does work in the declare args. put it there

examples/platform/silabs/efr32/BUILD.gn

@@ -58,7 +58,6 @@ assert(!(use_wf200 && chip_enable_openthread))
 
 if (chip_enable_wifi) {
   assert(use_rs9116 || use_wf200 || use_SiWx917)
-  enable_openthread_cli = false
   import("${chip_root}/src/platform/silabs/efr32/wifi_args.gni")
 
   if (use_rs9116) {
@@ -293,8 +292,7 @@ source_set("efr32-common") {
     sources += [ "LEDWidget.cpp" ]
   }
 
-  if (chip_enable_pw_rpc || chip_build_libshell || enable_openthread_cli ||
-      use_wf200 || use_rs9116) {
+  if (chip_enable_pw_rpc || chip_build_libshell || enable_openthread_cli) {
     sources += [ "uart.cpp" ]
   }
 

src/test_driver/efr32/BUILD.gn

@@ -73,13 +73,10 @@ silabs_executable("efr32_device_tests") {
     "${examples_common_plat_dir}/PigweedLogger.cpp",
     "${examples_common_plat_dir}/heap_4_silabs.c",
     "${examples_plat_dir}/init_efrPlatform.cpp",
+    "${examples_plat_dir}/uart.cpp",
     "src/main.cpp",
   ]
 
-  if (chip_enable_pw_rpc || chip_build_libshell || enable_openthread_cli) {
-    sources += [ "${examples_plat_dir}/uart.cpp" ]
-  }
-
   deps = [
     ":nl_test_service.nanopb_rpc",
     ":sdk",

third_party/silabs/efr32_sdk.gni

@@ -33,8 +33,9 @@ declare_args() {
 
   # Build openthread with prebuilt silabs lib
   use_silabs_thread_lib = false
-  enable_openthread_cli = true
 
+  # enable by default for thread/non-wifi-ncp builds
+  enable_openthread_cli = !(use_rs9116 || use_wf200 || use_SiWx917)
   kvs_max_entries = 255
 
   # Use Silabs factory data provider example.