crc-mi4: use const lookup table for crc

This doesn't touch external tools as I see no need for.

Change-Id: Ia69248c4b6a033c3772916525257e3540bddcffa
Reviewed-on: http://gerrit.rockbox.org/891
Tested: Sebastian Leonhardt <sebastian.leonhardt@web.de>
Reviewed-by: Marcin Bukat <marcin.bukat@gmail.com>