dt-bindings: mmc: synopsys-dw-mshc: add iommus for Intel SocFPGA

The DW MSHC node in Intel SocFPGA ARM64 DTS has iommus property, so
allow it to silence dtbs_check warnings:

  socfpga_n5x_socdk.dtb: mmc@ff808000: Unevaluated properties are not allowed ('iommus' was unexpected)

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231209171013.249972-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>