Prevent multiple inclusions of object files and rules

Prevent multiple inclusions of object files and rules

This removes 54 make warnings from the build

Change-Id: I94ac9875526febe2f95334c1c3971641c1d27f8f
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/338
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>