Docs: Updated target-file list to the new structure.

This patch updates the default file-target list for the
`find_tfm_root method`, used when the documentation is
build in standlone mode.

When sphinx-build is called directly, this method is
used to deterermine the project's root directory.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
Change-Id: I33d7918eff26f8d76492464705af6a8cfec2d994
diff --git a/tools/documentation/tfm_cmake_defaults.py b/tools/documentation/tfm_cmake_defaults.py
index 9aff5c6..9da42e1 100644
--- a/tools/documentation/tfm_cmake_defaults.py
+++ b/tools/documentation/tfm_cmake_defaults.py
@@ -33,7 +33,7 @@
 def find_tfm_root(start_dir=os.path.dirname(os.path.abspath(__file__)),
                   target_files=["license.rst",
                                 "dco.txt",
-                                "CommonConfig.cmake"],
+                                "toolchain_GNUARM.cmake"],
                   max_depth=5):
     """ Method which attempts to find the root of the project
     by traversing parent directoried and attempts to located each of the