msm: pcie: add new DRV commands for APPS to control PCIe L1ss sleep

Add support to synchronize PCIe L1ss sleep state between APPS
and DRV subsystem. This will remove any ambiguity of PCIe link
state for APPS when trying to enable/disable DRV.

Change-Id: Idb27a631a6eca3aa32a372e2e30235ef0ca10bf4
Signed-off-by: Tony Truong <truong@codeaurora.org>