Let devices specify transaction attributes when calling dma_buf_rw().

Keep the default MEMTXATTRS_UNSPECIFIED in the 2 callers.

Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211223115554.3155328-11-philmd@redhat.com>