[PPC] Fix compile failure do to introduction of PHY_POLL

PHY_POLL is defined in <linux/phy.h> include it in <linux/fsl_devices.h> so
board code will have it defined.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

include/linux/fsl_devices.h

@@ -19,6 +19,7 @@
 #define _FSL_DEVICE_H_
 
 #include <linux/types.h>
+#include <linux/phy.h>
 
 /*
  * Some conventions on how we handle peripherals on Freescale chips