net: extract function net_sntp_set_rtc() from sntp_handler()

Extract the code that sets the RTC clock from sntp_handler() in
net/sntp.c and make it a new function net_sntp_set_rtc() in
net/net-common.c. This will allow re-use with NET_LWIP.

According to [1] it is safe to assume that all devices have been
converted to DM_RTC so drop the useless code.

[1] https://lists.denx.de/pipermail/u-boot/2025-June/591376.html

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/net/sntp.c b/net/sntp.c
index 73d1d87..77cee00 100644
--- a/net/sntp.c
+++ b/net/sntp.c
@@ -57,8 +57,7 @@
 			 unsigned src, unsigned len)
 {
 	struct sntp_pkt_t *rpktp = (struct sntp_pkt_t *)pkt;
-	struct rtc_time tm;
-	ulong seconds;
+	u32 seconds;
 
 	debug("%s\n", __func__);
 
@@ -69,24 +68,8 @@
 	 * As the RTC's used in U-Boot support second resolution only
 	 * we simply ignore the sub-second field.
 	 */
-	memcpy(&seconds, &rpktp->transmit_timestamp, sizeof(ulong));
-
-	rtc_to_tm(ntohl(seconds) - 2208988800UL + net_ntp_time_offset, &tm);
-#ifdef CONFIG_DM_RTC
-	struct udevice *dev;
-	int ret;
-
-	ret = uclass_get_device(UCLASS_RTC, 0, &dev);
-	if (ret)
-		printf("SNTP: cannot find RTC: err=%d\n", ret);
-	else
-		dm_rtc_set(dev, &tm);
-#elif defined(CONFIG_CMD_DATE)
-	rtc_set(&tm);
-#endif
-	printf("Date: %4d-%02d-%02d Time: %2d:%02d:%02d\n",
-	       tm.tm_year, tm.tm_mon, tm.tm_mday,
-	       tm.tm_hour, tm.tm_min, tm.tm_sec);
+	memcpy(&seconds, &rpktp->transmit_timestamp, sizeof(seconds));
+	net_sntp_set_rtc(ntohl(seconds) - 2208988800UL + net_ntp_time_offset);
 
 	net_set_state(NETLOOP_SUCCESS);
 }