msm: pcie: add DRV enabled status for each RC

While performing a PCIe link hand-off to the DRV subsystem, it
is possible that the DRV subsystem itself could crash and
recover, whereas the host can remain unaware of that. Add the
ability to track the DRV enabled status for each root port.
This can ensure, for example, that the host does not send a DRV
disable command over to the DRV subsystem when it does not
expect one after a fresh boot-up.

Change-Id: Idede01c1cfa82073768883beafa90b4ea74b7c00
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>