m68k: Hook up rtc-generic

m68k has been a long time user of the generic RTC abstraction, so hook up
rtc-generic:
  - Create the "rtc-generic" platform device if mach_hwclk is set,
  - Add checks for mach_hwclk, in anticipation of RTC chip drivers being moved
    to drivers/rtc/.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
diff --git a/arch/m68k/include/asm/rtc.h b/arch/m68k/include/asm/rtc.h
index 5d3e038..a4d08ea 100644
--- a/arch/m68k/include/asm/rtc.h
+++ b/arch/m68k/include/asm/rtc.h
@@ -36,13 +36,16 @@
 	 * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
 	 * by the RTC when initially set to a non-zero value.
 	 */
-	mach_hwclk(0, time);
+	if (mach_hwclk)
+		mach_hwclk(0, time);
 	return RTC_24H;
 }
 
 static inline int set_rtc_time(struct rtc_time *time)
 {
-	return mach_hwclk(1, time);
+	if (mach_hwclk)
+		return mach_hwclk(1, time);
+	return -EINVAL;
 }
 
 static inline unsigned int get_rtc_ss(void)