PM / devfreq: rockchip-dfi: make register stride SoC specific

PM / devfreq: rockchip-dfi: make register stride SoC specific

The currently supported RK3399 has a stride of 20 between the channel
specific registers. Upcoming RK3588 has a different stride, so put
the stride into driver data to make it configurable.
While at it convert decimal 20 to hex 0x14 for consistency with RK3588
which has a register stride 0x4000 and we want to write that in hex
as well.

Link: https://lore.kernel.org/all/20231018061714.3553817-18-s.hauer@pengutronix.de/
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>