Replace includes of build.h with version.h

As build.h is an auto-generated file it was necessary to add it as
an explicit prerequisite in the Makefiles. When this was forgotten
abuild would sometimes fail with following error:

   fatal error: build.h: No such file or directory

Fix this error by compiling version.c into all stages.

Change-Id: I342f341077cc7496aed279b00baaa957aa2af0db
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7510
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>