dmaengine: loongson: New driver for the Loongson Multi-Channel DMA controller

dmaengine: loongson: New driver for the Loongson Multi-Channel DMA controller

This DMA controller appears in Loongson-2K0300 and Loongson-2K3000.

It is a chain multi-channel controller that enables data transfers from
memory to memory, device to memory, and memory to device, as well as
channel prioritization configurable through the channel configuration
registers.

In addition, there are slight differences between Loongson-2K0300 and
Loongson-2K3000, such as channel register offsets and the number of
channels.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/73bc32ba6249f1eef94fec9b349bc9efa98278ea.1772853681.git.zhoubinbin@loongson.cn
Signed-off-by: Vinod Koul <vkoul@kernel.org>