arm_adi_v5: Split ahbap_debugport_init

arm_adi_v5: Split ahbap_debugport_init

This function does two separate things, powering up the DP and setting
up a MEM-AP. But the DP needs to be powered before even searching for a
MEM-AP to initialize and targets may have multiple MEM-APs that need
initializing.

Split the function into dap_dp_init() and mem_ap_init() and change all
call sites to use the appropriate one.

Change-Id: I92f55e09754a93f3f01dd8e5aa1ffdf60c856126
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3151
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>