logic_pio: Build into a library

Object file logic_pio.o is always built.

Ideally the object file should only be built when required. This is
tricky, as that would be for archs which define PCI_IOBASE, but no common
config option exists for that.

For now, continue to always build but at least ensure the symbols are not
included in the vmlinux when not referenced.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>