jtag: only change state if necessary

All the other drivers will only change the state if required.
This brings all the other drivers inline with this behaviour.

The original issue relates to problems on xscale commit 7989000e09

Change-Id: Ifc90ec2eef68a70a14f37c00931a07982bfa200c
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1114
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/jtag/drivers/amt_jtagaccel.c

@@ -264,7 +264,10 @@ static void amt_jtagaccel_scan(bool ir_scan, enum scan_type type, uint8_t *buffe
 	else
 		amt_jtagaccel_end_state(TAP_DRSHIFT);
 
-	amt_jtagaccel_state_move();
+	/* Only move if we're not already there */
+	if (tap_get_state() != tap_get_end_state())
+		amt_jtagaccel_state_move();
+
 	amt_jtagaccel_end_state(saved_end_state);
 
 	/* handle unaligned bits at the beginning */

src/jtag/drivers/arm-jtag-ew.c

@@ -355,7 +355,10 @@ static void armjtagew_scan(bool ir_scan,
 	/* Move to appropriate scan state */
 	armjtagew_end_state(ir_scan ? TAP_IRSHIFT : TAP_DRSHIFT);
 
-	armjtagew_state_move();
+	/* Only move if we're not already there */
+	if (tap_get_state() != tap_get_end_state())
+		armjtagew_state_move();
+
 	armjtagew_end_state(saved_end_state);
 
 	/* Scan */

src/jtag/drivers/buspirate.c

@@ -520,7 +520,10 @@ static void buspirate_scan(bool ir_scan, enum scan_type type,
 	saved_end_state = tap_get_end_state();
 
 	buspirate_end_state(ir_scan ? TAP_IRSHIFT : TAP_DRSHIFT);
-	buspirate_state_move();
+
+	/* Only move if we're not already there */
+	if (tap_get_state() != tap_get_end_state())
+		buspirate_state_move();
 
 	buspirate_tap_append_scan(scan_size, buffer, command);