msm: pcie: Save and restore config space for RC

PCI framework tries to save the config space of PCIe Root Complex
(RC) after PCIe link is down and thus overrides the saved state by
PCIe bus driver. Some info is lost because of this, which happens
regardless of whether the suspend is triggered by client driver or
not. Thus, the change here is to save the config space content to
a local copy and restore the config space from it.

Change-Id: I0081f6ef9b68573e9e0c5c4e906a25be0788e318
Signed-off-by: Yan He <yanhe@codeaurora.org>