xtensa: enable HAVE_DMA_CONTIGUOUS

Enable HAVE_DMA_CONTIGUOUS, reserve contiguous memory at bootmem_init,
use dma_alloc_from_contiguous and dma_release_from_contiguous in
xtensa_dma_alloc/free.
This allows for big contiguous DMA buffer allocation from designated
area configured in the device tree.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/mm/init.c

@@ -26,6 +26,7 @@
 #include <linux/nodemask.h>
 #include <linux/mm.h>
 #include <linux/of_fdt.h>
+#include <linux/dma-contiguous.h>
 
 #include <asm/bootparam.h>
 #include <asm/page.h>
@@ -60,6 +61,7 @@ void __init bootmem_init(void)
 	max_low_pfn = min(max_pfn, MAX_LOW_PFN);
 
 	memblock_set_current_limit(PFN_PHYS(max_low_pfn));
+	dma_contiguous_reserve(PFN_PHYS(max_low_pfn));
 
 	memblock_dump_all();
 }