PCI: Add ACS quirk for Loongson PCIe

Loongson PCIe Root Ports don't advertise an ACS capability, but they do not
allow peer-to-peer transactions between Root Ports. Add an ACS quirk so
each Root Port can be in a separate IOMMU group.

Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20250403040756.720409-1-chenhuacai@loongson.cn