MIPS: Loongson64: Drop setup_pcimap

setup_pcimap is used to setup address windows for Loongson-3
built-in PCI-X controller, but this function is never been used
in the real world and lack of support in kernel.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: chenhe@lemote.com