We can reuse it for pciehp probing.

-v2: according to Kenji, fix crs timeout checking, and export the function
     for later use when pciehp is compiled as a module.
Suggested-by: NMatthew Wilcox <matthew@wil.cx>
Signed-off-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>