dma mapping : export caller to vmallocinfo

For example on arm64 board, this add info to "user" entries in vmallocinfo

Before :
[...]
0xffffff8008997000 0xffffff80089d8000 266240 user
[...]

Afer :
[...]
0xffffff8008997000 0xffffff80089d8000 266240 atomic_pool_init+0x0/0x1d8 user
[...]

This help to debug mapping issues, and is consistent with others entries
(ioremap, vmalloc, ...) that already provide caller.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Matthieu CASTET <matthieu.castet@parrot.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/dma-mapping.c

@@ -166,7 +166,7 @@ static void *__dma_alloc(struct device *dev, size_t size,
 	/* create a coherent mapping */
 	page = virt_to_page(ptr);
 	coherent_ptr = dma_common_contiguous_remap(page, size, VM_USERMAP,
-						   prot, NULL);
+						   prot, __builtin_return_address(0));
 	if (!coherent_ptr)
 		goto no_map;