jtag/swd: extend ap_delay_hint parameter comments

Assure that zero is passed in ap_delay_hint in case of DP r/w.

Change-Id: I5cd53b99950a7f1398b88f7394b3e66530803479
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/8689
Tested-by: jenkins

src/jtag/swd.h

@@ -270,6 +270,7 @@ struct swd_driver {
 	 * @param Where to store value to read from register
 	 * @param ap_delay_hint Number of idle cycles that may be
 	 * needed after an AP access to avoid WAITs
+	 * or zero in case of DP read.
 	 */
 	void (*read_reg)(uint8_t cmd, uint32_t *value, uint32_t ap_delay_hint);
 
@@ -280,6 +281,7 @@ struct swd_driver {
 	 * @param Value to be written to the register
 	 * @param ap_delay_hint Number of idle cycles that may be
 	 * needed after an AP access to avoid WAITs
+	 * or zero in case of DP write.
 	 */
 	void (*write_reg)(uint8_t cmd, uint32_t value, uint32_t ap_delay_hint);