MIPS/PCI: Let Loongson-3 pci_ops access extended config space

Original Loongson-3 pci_ops can only access standard pci config space,
this patch let it be able to access extended pci config space.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
[paul.burton@mips.com: Tweaks to fix checkpatch warnings, reverse xmas tree]
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/20707/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: Huacai Chen <chenhuacai@gmail.com>