arm64: dts: ls2080a: Add 'dma-coherent' for ls2080a PCI nodes

The 'dma-coherent' indicates that the hardware IP block can ensure
the coherency of the data transferred from/to the IP block. This
can avoid the software cache flush/invalid actions, and improve
the performance significantly.

The PCI IP block of ls2080a has this capability, so adding this
feature to improve the PCI performance.

Signed-off-by: Liu Gang <Gang.Liu@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>