build system: Fix regression after adding cbfs-files alignment

Commit 5839635a broke cbfs file-position, probably resulting with
non-booting Intel platforms using mrc.bin and the risk of AGESA
with HAVE_ACPI_RESUME corrupting cbfs as s3nv.bin was not properly
located.

Change-Id: I6ca7a3cdf8dfe40bf47da6c6071ef7b1f42a32b4
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7920
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>