msm: pcie: add support to notify client early for SSR

When other subsystems crash, PCIe will get an early notificaion
from SSR framework and relay it to the clients. Clients will
have the ability to resume the link or clean up.

Change-Id: Iabee769d1b07c5174a18db56b7e1094b86564884
Signed-off-by: Tony Truong <truong@codeaurora.org>