rtc: generic: allow building on all architectures

There are four architectures using this driver, but since we can
build it with COMPILE_TEST, we should try dealing with the absence
of the asm/rtc.h header file, to avoid getting a build error:

drivers/rtc/rtc-generic.c:12:21: fatal error: asm/rtc.h: No such file or directory

This creates an alternative use of the driver, allowing architectures
to pass a set of rtc_class_ops in platform data. We can convert the
four architectures to use this and then remove the original
code.

Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/rtc-generic.c

···
 #include <linux/platform_device.h>
 #include <linux/rtc.h>
 
+#if defined(CONFIG_M68K) || defined(CONFIG_PARISC) || \
+    defined(CONFIG_PPC) || defined(CONFIG_SUPERH32)
 #include <asm/rtc.h>
 
 static int generic_get_time(struct device *dev, struct rtc_time *tm)
···
 	.read_time = generic_get_time,
 	.set_time = generic_set_time,
 };
+#else
+#define generic_rtc_ops *(struct rtc_class_ops*)NULL
+#endif
 
 static int __init generic_rtc_probe(struct platform_device *dev)
 {
 	struct rtc_device *rtc;
+	const struct rtc_class_ops *ops;
+
+	ops = dev_get_platdata(&dev->dev);
+	if (!ops)
+		ops = &generic_rtc_ops;
 
 	rtc = devm_rtc_device_register(&dev->dev, "rtc-generic",
-					&generic_rtc_ops, THIS_MODULE);
+					ops, THIS_MODULE);
 	if (IS_ERR(rtc))
 		return PTR_ERR(rtc);