rtc: move power of 2 periodic frequency check down into drivers

Move the power of 2 check on frequencies down into individual rtc drivers

This is to allow for non power of 2 real time clock periodic interrupts
such as those on the pxa27x to be found in the new pxa27x-rtc driver

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-sh.c

@@ -24,6 +24,7 @@
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/io.h>
+#include <linux/log2.h>
 #include <asm/rtc.h>
 
 #define DRV_NAME	"sh-rtc"
@@ -551,6 +552,8 @@ static int sh_rtc_irq_set_state(struct device *dev, int enabled)
 
 static int sh_rtc_irq_set_freq(struct device *dev, int freq)
 {
+	if (!is_power_of_2(freq))
+		return -EINVAL;
 	return sh_rtc_ioctl(dev, RTC_IRQP_SET, freq);
 }