arm_adi_v5: Rewrite MEM-AP transfer implementation

arm_adi_v5: Rewrite MEM-AP transfer implementation

Create a single pair of relatively simple functions to handle all variants
of MEM-AP transfers. This replaces the many separate functions that
handled different access sizes and packed or non-packed transfers, which
were all implemented rather differently.

With this single implementation, performance should be more consistent,
regardless of transfer type.

Change-Id: I89960e437fc6ba68a389c074fab8eac91abcf844
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1658
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>