FSL: Clean up board/freescale/common/Makefile

FSL: Clean up board/freescale/common/Makefile

Each file that can be built here now follows some
CONFIG_ option so that they are appropriately built
or not, as needed.  And CONFIG_ defines were added
to various board config files to make sure that happens.

The other board/freescale/*/Makefiles no longer need
to reach up and over into ../common to build their
individually needed files any more.

Boards that are CDS specific were renamed with cds_ prefix.

Signed-off-by: Jon Loeliger <jdl@freescale.com>