riscv: dts: sophgo: Add dma-coherent to SG2042 PCIe controllers

riscv: dts: sophgo: Add dma-coherent to SG2042 PCIe controllers

SG2042's PCIe root complexes are cache-coherent with the CPU. Mark all
four PCIe controller nodes (pcie_rc0 through pcie_rc3) as dma-coherent
so the kernel uses coherent DMA mappings instead of non-coherent bounce
buffering.

Cc: stable@vger.kernel.org
Signed-off-by: Han Gao <gaohan@iscas.ac.cn>
Link: https://patch.msgid.link/20260331171248.973014-3-gaohan@iscas.ac.cn
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>