arm_adi_v5: Fix packed and unaligned memory writes

arm_adi_v5: Fix packed and unaligned memory writes

For packed and/or unaligned accesses, the write functions reordered the
source buffer in place. Causing in the best case a segfault, in the worst
case silent data corruption.

Rewrite the data fetching to directly match the byte lane mapping
according to IHI0031C, without destroying the buffer.

Also slightly clean up variable usage and harmonize all the write
functions.

Change-Id: I9a01cfc5578653f9ec02043ff6b61a7a20f90d67
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1646
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>