CMake: unit-tests: Make hal stubs only depend on headers it uses

Previously the hal stub library depended on `mbed-headers`, which
is a collection of all available headers in mbed-os. To make it easier
to separate the library, only depend on the headers we're using.

hal/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -32,6 +32,8 @@ target_link_options(mbed-stubs-hal
 
 target_link_libraries(mbed-stubs-hal
     PRIVATE
-        mbed-headers
+        mbed-headers-base
+        mbed-headers-hal
+        mbed-headers-platform
         mbed-stubs-headers
 )