microblaze: Fix mmap for cache coherent memory

When running in non-cache coherent configuration the memory that was
allocated with dma_alloc_coherent() has a custom mapping and so there is no
1-to-1 relationship between the kernel virtual address and the PFN. This
means that virt_to_pfn() will not work correctly for those addresses and the
default mmap implementation in the form of dma_common_mmap() will map some
random, but not the requested, memory area.

Fix this by providing a custom mmap implementation that looks up the PFN
from the page table rather than using virt_to_pfn.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/include/asm/pgtable.h

@@ -565,6 +565,7 @@ void consistent_free(size_t size, void *vaddr);
 void consistent_sync(void *vaddr, size_t size, int direction);
 void consistent_sync_page(struct page *page, unsigned long offset,
 	size_t size, int direction);
+unsigned long consistent_virt_to_pfn(void *vaddr);
 
 void setup_memory(void);
 #endif /* __ASSEMBLY__ */