hwdriver: Add SR_CONF_CLOCK_EDGE option.

Allow the edge of an external clock input to be configured by
means of an SR_CONF_CLOCK_EDGE configuration setting.  This is
a string option with the same format as SR_CONF_TRIGGER_SLOPE.

hwdriver.c

@@ -118,6 +118,8 @@ static struct sr_config_info sr_config_info_data[] = {
 		"Over-current protection", NULL},
 	{SR_CONF_LIMIT_SAMPLES, SR_T_UINT64, "limit_samples",
 		"Sample limit", NULL},
+	{SR_CONF_CLOCK_EDGE, SR_T_CHAR, "clock_edge",
+		"Clock edge", NULL},
 	{0, 0, NULL, NULL, NULL},
 };
 

libsigrok.h

@@ -834,6 +834,9 @@ enum {
 	/** Over-current protection (OCP) */
 	SR_CONF_OVER_CURRENT_PROTECTION,
 
+	/** Choice of clock edge for external clock ("r" or "f"). */
+	SR_CONF_CLOCK_EDGE,
+
 	/*--- Special stuff -------------------------------------------------*/
 
 	/** Scan options supported by the driver. */