arm64: dts: NS2: Add dma-coherent to relevant DT entries

Cache related issues with DMA rings and performance issues related to
caching are being caused by not properly setting the "dma-coherent" flag
in the device tree entries.  Adding it here to correct the issue.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Fixes: fd5e5dd5 ("arm64: dts: Add PCIe0 and PCIe4 DT nodes for NS2")
Fixes: dddc3c9d ("arm64: dts: NS2: add AMAC ethernet support")
Fixes: e7924914 ("arm64: dts: Add Broadcom Northstar2 device tree entries for PDC driver")
Fixes: ac9aae00 ("arm64: dts: Add SATA3 AHCI and SATA3 PHY DT nodes for NS2")
Fixes: efc87767 ("arm64: dts: Add SDHCI DT node for NS2")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>