msm: pcie: Read vendor ID and device ID from PCIe core

PCIe devices can have different vendor IDs and device IDs. Thus,
add the support to read the vendor ID and device ID of a PCIe
device from PCIe core.

Change-Id: I582750289537159b240f3e313fd07151b13bd27c
Signed-off-by: Yan He <yanhe@codeaurora.org>