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
1 file changed