dmaengine: add peripheral configuration

Some complex dmaengine controllers have capability to program the
peripheral device, so pass on the peripheral configuration as part of
dma_slave_config

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

include/linux/dmaengine.h

···
  * @slave_id: Slave requester id. Only valid for slave channels. The dma
  * slave peripheral will have unique id as dma requester which need to be
  * pass as slave config.
+ * @peripheral_config: peripheral configuration for programming peripheral
+ * for dmaengine transfer
+ * @peripheral_size: peripheral configuration buffer size
  *
  * This struct is passed in as configuration data to a DMA engine
  * in order to set up a certain channel for DMA transport at runtime.
···
 	u32 dst_port_window_size;
 	bool device_fc;
 	unsigned int slave_id;
+	void *peripheral_config;
+	size_t peripheral_size;
 };
 
 /**