dma: mmp_pdma: add filter function

PXA peripherals need to obtain specific DMA request ids which will
eventually be stored in the DRCMR register.

Currently, clients are expected to store that number inside the slave
config block as slave_id, which is unfortunately incompatible with the
way DMA resources are handled in DT environments.

This patch adds a filter function which stores the filter parameter
passed in by of-dma.c into the channel's drcmr register.

For backward compatability, cfg->slave_id is still used if set to
a non-zero value.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

include/linux/dma/mmp-pdma.h

@@ -0,0 +1,15 @@
+#ifndef _MMP_PDMA_H_
+#define _MMP_PDMA_H_
+
+struct dma_chan;
+
+#ifdef CONFIG_MMP_PDMA
+bool mmp_pdma_filter_fn(struct dma_chan *chan, void *param);
+#else
+static inline bool mmp_pdma_filter_fn(struct dma_chan *chan, void *param)
+{
+	return false;
+}
+#endif
+
+#endif /* _MMP_PDMA_H_ */