msm: pcie: Add support for various clients for PM transition

It is valid that various PCIe endpoints on different Root Complexes (RCs)
may have the same bus number. Thus, add the support here to distinguish
different RCs during Power Management transition by PCIe clients.

Change-Id: I0c1d5a81a878a9b4554c934a7e06a418111a1b38
Signed-off-by: Yan He <yanhe@codeaurora.org>