cnss: Save/restore target PCIe config space during suspend/resume

In some cases PCIe framework fails to restore the target PCIe config
space during suspend/resume, so add the support that CNSS platform
driver can save/restore it.

Change-Id: I5522eaba98421df6734b596f62174e159450c367
CRs-fixed: 697607
Signed-off-by: Yue Ma <yuem@codeaurora.org>