iommu/tegra: gart: Prepend error/debug messages with "gart:"

GART became a part of Memory Controller, hence now the drivers device
is Memory Controller and not GART. As a result all printed messages are
prepended with the "tegra-mc 7000f000.memory-controller:", so let's
prepend GART's messages with "gart:" in order to differentiate them
from the MC.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/tegra-gart.c

@@ -19,6 +19,8 @@
  * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#define dev_fmt(fmt)	"gart: " fmt
+
 #include <linux/io.h>
 #include <linux/iommu.h>
 #include <linux/list.h>