The dmamux register is located within the system controller.

Without syscon, we need an extra helper in order to give write access to
this register to a dmamux driver.
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>
Acked-by: NStephen Boyd <sboyd@kernel.org>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220427095653.91804-5-miquel.raynal@bootlin.comSigned-off-by: NVinod Koul <vkoul@kernel.org>