dt-bindings: ufs: exynos-ufs: add io-coherency property

Add "samsung,sysreg" regmap and the offset to the ufs shareability
register for setting io coherency of the samsung ufs. "dma-coherent"
property is also required because the driver code needs to know.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Chanho Park <chanho61.park@samsung.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211018124216.153072-13-chanho61.park@samsung.com