microblaze_mmu_v2: Update dma.h for MMU

Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/include/asm/dma.h

@@ -9,8 +9,13 @@
 #ifndef _ASM_MICROBLAZE_DMA_H
 #define _ASM_MICROBLAZE_DMA_H
 
+#ifndef CONFIG_MMU
 /* we don't have dma address limit. define it as zero to be
  * unlimited. */
 #define MAX_DMA_ADDRESS		(0)
+#else
+/* Virtual address corresponding to last available physical memory address.  */
+#define MAX_DMA_ADDRESS (CONFIG_KERNEL_START + memory_size - 1)
+#endif
 
 #endif /* _ASM_MICROBLAZE_DMA_H */