xtensa: Provide dummy dma_mmap_coherent() and dma_get_sgtable()

xtensa/allmodconfig:

drivers/media/v4l2-core/videobuf2-dma-contig.c: In function ‘vb2_dc_mmap’:
drivers/media/v4l2-core/videobuf2-dma-contig.c:204: error: implicit declaration of function ‘dma_mmap_coherent’
drivers/media/v4l2-core/videobuf2-dma-contig.c: In function ‘vb2_dc_get_base_sgt’:
drivers/media/v4l2-core/videobuf2-dma-contig.c:387: error: implicit declaration of function ‘dma_get_sgtable’

For architectures using dma_map_ops, dma_mmap_coherent() and
dma_get_sgtable() are provided in <asm-generic/dma-mapping-common.h>.

Xtensa does not use dma_map_ops, hence it should implement them itself.
For now, use dummy implementations that just return -EINVAL, until the API
has been finalized.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: linux-xtensa@linux-xtensa.org
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

arch/xtensa/include/asm/dma-mapping.h

@@ -170,4 +170,19 @@ dma_cache_sync(struct device *dev, void *vaddr, size_t size,
 	consistent_sync(vaddr, size, direction);
 }
 
+/* Not supported for now */
+static inline int dma_mmap_coherent(struct device *dev,
+				    struct vm_area_struct *vma, void *cpu_addr,
+				    dma_addr_t dma_addr, size_t size)
+{
+	return -EINVAL;
+}
+
+static inline int dma_get_sgtable(struct device *dev, struct sg_table *sgt,
+				  void *cpu_addr, dma_addr_t dma_addr,
+				  size_t size)
+{
+	return -EINVAL;
+}
+
 #endif	/* _XTENSA_DMA_MAPPING_H */