mtd: 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: Tejun Heo <tj@kernel.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/nand/mpc5121_nfc.c b/drivers/mtd/nand/mpc5121_nfc.c
index f713b15..3d0867d 100644
--- a/drivers/mtd/nand/mpc5121_nfc.c
+++ b/drivers/mtd/nand/mpc5121_nfc.c
@@ -27,6 +27,7 @@
 
 #include <linux/module.h>
 #include <linux/clk.h>
+#include <linux/gfp.h>
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>