Follow the model of the Linux kernel for adding arch
specific CFLAGS by using the Makefile and Kbuild combination
in the arch/<arch> directory.
This will also allow adding architecture specific targets and is
easy to maintain when alongside the architecture.
Change-Id: If51a78e8845baa71d9090c4a4f49fcd013354840
Signed-off-by: Anas Nashif <anas.nashif@intel.com>