arm_adi_v5: fix mem_ap_read_buf_u32() JTAG nastiness..

Moved JTAG code out of transport-neutral file (arm_adi_v5.c) into
transport specific file (adi_v5_jtag.c).
Added ap_block_read to dap_ops interface (arm_adi_v5.h) to support
the move.

Change-Id: I796d3984f138aad052b97c77ac9c12ffd1158f74
Signed-off-by: mike brown <mike@theshedworks.org.uk>
Reviewed-on: http://openocd.zylin.com/1277
Tested-by: jenkins
Reviewed-by: Michel JAOUEN <michel.jaouen@stericsson.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>