Revert "Make all build results depend on all makefiles"

Seems to have unintended side-effects on the build system such as
rebuilding certain parts of TF even though nothing has changed.

This reverts commit c6f651f9.

Change-Id: I1472e6c630cb6371ec629b7d97a5748d9a6fd096
Signed-off-by: Dimitris Papastamos <dimitris.papastamos@arm.com>