msm: pcie: allow client to turn off link during linkdown

The client driver can recover the link during linkdown callback.
The change here allows the client to turn off the power of link
when the link status is down.

Change-Id: Ia036199c39c66a6a6e258318b878c9c966c11260
Signed-off-by: Tony Truong <truong@codeaurora.org>