hla_target: allow non-intrusive profiling on cortex-m

Leverages the existing work that added profiling via DWT_PCSR.

hla_target doesn't have direct access to the mem_ap for doing a bulk
repeated read, but simply reading the DWT_PCSR register repeatedly is
still ~2 order of magnitude faster than halt/resume.

Change-Id: Ibe451aa95143694398370fdad6939cfb6191d56f
Signed-off-by: Karl Palsson <karlp@tweak.net.au>
Reviewed-on: http://openocd.zylin.com/4220
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>

src/target/hla_target.c

@@ -814,4 +814,5 @@ struct target_type hla_target = {
 	.remove_breakpoint = cortex_m_remove_breakpoint,
 	.add_watchpoint = cortex_m_add_watchpoint,
 	.remove_watchpoint = cortex_m_remove_watchpoint,
+	.profiling = cortex_m_profiling,
 };