scpi-dmm: add period measurement support for XDM2041

It's displays period in seconds instead of frequency in Hz

Author: evgeny-boger

src/hardware/scpi-dmm/api.c

@@ -213,6 +213,7 @@ static const struct mqopt_item mqopts_owon_xdm2041[] = {
 	{ SR_MQ_VOLTAGE, SR_MQFLAG_DC | SR_MQFLAG_DIODE, "DIOD", "DIOD", -4, FLAG_NO_RANGE, },
 	{ SR_MQ_TEMPERATURE, 0, "TEMP", "TEMP", NO_DFLT_PREC, FLAGS_NONE, },
 	{ SR_MQ_FREQUENCY, 0, "FREQ", "FREQ", NO_DFLT_PREC, FLAG_NO_RANGE, },
+	{ SR_MQ_TIME, 0, "PER", "PER", NO_DFLT_PREC, FLAG_NO_RANGE, },
 	{ SR_MQ_CAPACITANCE, 0, "CAP", "CAP", NO_DFLT_PREC, FLAGS_NONE, },
 };