Standalone Apps: Standalone apps should need only exports.h.

Modify exports.h to remove its dependencies on other files, thus
enabling standalone apps to require only exports.h from the U-Boot
source tree.  This appears to be the intent based on the following
note: http://lists.denx.de/pipermail/u-boot/2010-January/067174.html



Signed-off-by: Mike Partington <mparting@lexmark.com>