iommu/dma: Add some missing #includes

dma-iommu.c was naughtily relying on an implicit transitive #include of
linux/vmalloc.h, which is apparently not present on some architectures.
Add that, plus a couple more headers for other functions which are used
similarly.
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/dma-iommu.c

@@ -21,10 +21,13 @@
 
 #include <linux/device.h>
 #include <linux/dma-iommu.h>
+#include <linux/gfp.h>
 #include <linux/huge_mm.h>
 #include <linux/iommu.h>
 #include <linux/iova.h>
 #include <linux/mm.h>
+#include <linux/scatterlist.h>
+#include <linux/vmalloc.h>
 
 int iommu_dma_init(void)
 {