davinci: update gfp/slab.h includes

Implicit slab.h inclusion via percpu.h is about to go away.  Make sure
gfp.h or slab.h is included as necessary.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>

drivers/rtc/rtc-davinci.c

@@ -29,6 +29,7 @@
 #include <linux/bcd.h>
 #include <linux/platform_device.h>
 #include <linux/io.h>
+#include <linux/slab.h>
 
 /*
  * The DaVinci RTC is a simple RTC with the following