Create mbed-wifi target instantly instead of lazily

Reasons for this change:
1. One dummy 'mbed-wifi' target will add little to compile time.
2. The location where the 'mbed-wifi' target is created is now fixed to the
   top directory. CMake commands e.g. add_custom_command are required to
   invoke in the same directory as where the 'mbed-wifi' target is created,
   and can be invoked consistently in this fixed top directory.

Author: ccli8

connectivity/drivers/wifi/CMakeLists.txt

@@ -1,24 +1,25 @@
 # Copyright (c) 2020-2021 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-# The 'mbed-wifi' target is lazily created because there might not be any subdirectories needing it at all.
-macro(create_mbed_wifi_target)
-	if(NOT TARGET mbed-wifi)
-		add_library(mbed-wifi STATIC EXCLUDE_FROM_ALL)
+# The 'mbed-wifi' target is created instantly instead of lazily for below reasons:
+# 1. One dummy 'mbed-wifi' target will add little to compile time.
+# 2. The location where the 'mbed-wifi' target is created is now fixed to the
+#    top directory. CMake commands e.g. add_custom_command are required to
+#    invoke in the same directory as where the 'mbed-wifi' target is created,
+#    and can be invoked consistently in this fixed top directory.
+add_library(mbed-wifi STATIC EXCLUDE_FROM_ALL)
+
+target_link_libraries(mbed-wifi
+    PUBLIC
+        mbed-rtos-flags
+        mbed-netsocket-api
+)
 
-		target_link_libraries(mbed-wifi
-		    PUBLIC
-		        mbed-rtos-flags
-		        mbed-netsocket-api
-		)
-	endif()
-endmacro()
 
 
 # The WICED subdirectory is for wifi drivers developed using Infineon WICED framework.
 # https://community.infineon.com/t5/Knowledge-Base-Articles/WICED-Wi-Fi-FAQ/ta-p/247356
 if("WICED" IN_LIST MBED_TARGET_LABELS)
-	create_mbed_wifi_target()
     add_subdirectory(TARGET_WICED EXCLUDE_FROM_ALL)
 endif()
 
@@ -27,12 +28,10 @@ if("STM" IN_LIST MBED_TARGET_LABELS)
 endif()
 
 if("WHD" IN_LIST MBED_TARGET_LABELS)
-	create_mbed_wifi_target()
     add_subdirectory(COMPONENT_WHD EXCLUDE_FROM_ALL)
 endif()
 
 if("COMPONENT_ESPRESSIF_ESP8266=1" IN_LIST MBED_TARGET_DEFINITIONS)
-	create_mbed_wifi_target()
     add_subdirectory(COMPONENT_ESPRESSIF_ESP8266)
 endif()
 

connectivity/drivers/wifi/TARGET_STM/CMakeLists.txt

@@ -2,6 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0
 
 if("EMW3080B" IN_LIST MBED_TARGET_LABELS)
-    create_mbed_wifi_target()
     add_subdirectory(COMPONENT_EMW3080B EXCLUDE_FROM_ALL)
 endif()