dmaengine: rcar-dmac: Add for_each_rcar_dmac_chan() helper

dmaengine: rcar-dmac: Add for_each_rcar_dmac_chan() helper

Add a helper macro for iterating over all DMAC channels, taking into
account the channel mask.  Use it where appropriate, to simplify code.

Restore "reverse Christmas tree" order of local variables while adding a
new variable.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20210128084455.2237256-3-geert+renesas@glider.be
Signed-off-by: Vinod Koul <vkoul@kernel.org>