armv4_5: Integrate build of checksum code

Add rules to build armv4_5_crc.inc, and convert the code to target
endianness the least intrusive way.

Change-Id: I7452b2c7e679dae14f9cda5f89bc81c16fc12cad
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-on: http://openocd.zylin.com/3473


Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Tested-by: jenkins