sh: dma: Correct the number of DMA channels for SH7709

According to the hardware manual [1], the DMAC found in the SH7709 SoC
features only 4 channels. While at it, also sort the existing targets.

[1] https://www.renesas.com/us/en/document/mah/sh7709s-group-hardware-manual (p. 373)

Signed-off-by: Artur Rojek <contact@artur-rojek.eu>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20230527164452.64797-4-contact@artur-rojek.eu
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>