arm64: dts: Update Broadcom NS2 to generic IOMMU binding

With the "mmu-masters" property now deprecated and optional, the
generic binding offers a more efficient way to specify no masters.

CC: Ray Jui <rjui@broadcom.com>
CC: Scott Branden <sbranden@broadcom.com>
CC: Jon Mason <jonmason@broadcom.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm64/boot/dts/broadcom/ns2.dtsi

@@ -248,7 +248,7 @@ smmu: mmu@64000000 {
 				     <GIC_SPI 260 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 261 IRQ_TYPE_LEVEL_HIGH>,
 				     <GIC_SPI 262 IRQ_TYPE_LEVEL_HIGH>;
-			mmu-masters;
+			#iommu-cells = <1>;
 		};
 
 		pinctrl: pinctrl@6501d130 {