cortex_a: fix cortex_a_assert_reset() if srst_gates_jtag

The cortex_a specific assert_reset function must only apply nSRST if
the reset configuration states that JTAG can be used while nSRST is
asserted.

Change-Id: If604a65fdea5bcb46ec723ada547a4e8d6fa8c59
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>
Reviewed-on: http://openocd.zylin.com/3356
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/target/cortex_a.c

@@ -1912,7 +1912,9 @@ static int cortex_a_assert_reset(struct target *target)
 		/* REVISIT handle "pulls" cases, if there's
 		 * hardware that needs them to work.
 		 */
-		jtag_add_reset(0, 1);
+		if (target->reset_halt)
+			if (jtag_get_reset_config() & RESET_SRST_NO_GATING)
+				jtag_add_reset(0, 1);
 	} else {
 		LOG_ERROR("%s: how to reset?", target_name(target));
 		return ERROR_FAIL;