armv4_5: Integrate build of erase check code

Add rules to build armv4_5_erase_check.inc, and convert the code to
target endianness the least intrusive way.

Drop an unused word from the assembler sources to make the ARM bytecode
fully match that of armv4_5.c and to not break ARMv4 assumptions.

This completes the build rules for contrib/loaders/erase_check directory.

Change-Id: I36be7a944e26142088195fa3fb072d4e577bf328
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-on: http://openocd.zylin.com/3135


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