msm: pcie: add the option for client to avoid PCIe suspend

The PCIe client has the requirement to keep PCIe link on when the
CPUs go to power collapse. Add the support here for client driver
to keep PCIe link up during the system suspend.

Change-Id: I886990072c9c72c57e30c5c0cceb7eaedca071e6
Signed-off-by: Yan He <yanhe@codeaurora.org>