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/net-common.c b/net/net-common.c
index e01b0da..b064557 100644
--- a/net/net-common.c
+++ b/net/net-common.c
@@ -1,5 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0
+
+#include <dm/uclass.h>
 #include <net-common.h>
+#include <linux/time.h>
+#include <rtc.h>
 
 void copy_filename(char *dst, const char *src, int size)
 {
@@ -25,3 +29,22 @@
 	wget_info = info ? info : &default_wget_info;
 	return wget_do_request(dst_addr, uri);
 }
+
+void net_sntp_set_rtc(u32 seconds)
+{
+	struct rtc_time tm;
+	struct udevice *dev;
+	int ret;
+
+	rtc_to_tm(seconds, &tm);
+
+	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);
+
+	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);
+}