PCI: Add Loongson vendor ID

Add the Loongson vendor ID to pci_ids.h to be used by the controller
driver in the future.

The Loongson vendor ID can be found at the following link:
https://git.kernel.org/pub/scm/utils/pciutils/pciutils.git/tree/pci.ids

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>