Add support for the JZ4760 and JZ4760B SoCs.

Both SoCs have only 5 DMA channels per chip. The JZ4760B introduced the
DCKES/DCKEC registers.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20210120105322.16116-2-paul@crapouillou.netSigned-off-by: Vinod Koul <vkoul@kernel.org>