drm/msm: deal with mach/iommu.h removal

We still need an API exported by msm iommu driver (but not visible in
any public header anymore).  For now, just declare the prototype
ourselves, but when msm iommu driver provides a better option, use that
instead.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_drv.c

@@ -18,8 +18,6 @@
 #include "msm_drv.h"
 #include "msm_gpu.h"
 
-#include <mach/iommu.h>
-
 static void msm_fb_output_poll_changed(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
@@ -62,6 +60,8 @@ int msm_iommu_attach(struct drm_device *dev, struct iommu_domain *iommu,
 	int i, ret;
 
 	for (i = 0; i < cnt; i++) {
+		/* TODO maybe some day msm iommu won't require this hack: */
+		struct device *msm_iommu_get_ctx(const char *ctx_name);
 		struct device *ctx = msm_iommu_get_ctx(names[i]);
 		if (!ctx)
 			continue;