[ARM] pxa/z2: fix missing include in battery driver

Remove redundant includes and add slab.h to fix problem with building.
Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>

drivers/power/z2_battery.c

@@ -9,19 +9,13 @@
  *
  */
 
-#include <linux/init.h>
-#include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/platform_device.h>
-#include <linux/power_supply.h>
-#include <linux/i2c.h>
-#include <linux/spinlock.h>
-#include <linux/interrupt.h>
 #include <linux/gpio.h>
+#include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
-#include <asm/irq.h>
-#include <asm/mach/irq.h>
+#include <linux/power_supply.h>
+#include <linux/slab.h>
 #include <linux/z2_battery.h>
 
 #define	Z2_DEFAULT_NAME	"Z2"