target/zynqmp : Add AXI AP access port

The Xilinx Zynq UltraScale+ SoC have an "AXI-AP" access port for direct memory accesses without halting CPUs.

Change-Id: I6303331c217795657575de4759444938e775dee1
Signed-off-by: Olivier DANET <odanet@caramail.com>
Reviewed-on: http://openocd.zylin.com/6263
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

tcl/target/xilinx_zynqmp.cfg

@@ -92,6 +92,8 @@ for { set _core 0 } { $_core < $_cores } { incr _core } {
     eval $_command
 }
 
+target create uscale.axi mem_ap -dap uscale.dap -ap-num 0
+
 eval $_smp_command
 targets $_TARGETNAME.0