phy: msm: ssusb: Add support for cable_connected flag

Currently the phy-msm-ssusb driver sets the POWERDOWN bit and
turns off the clocks and regulators as a part of suspend
irrespective of whether cable is connected or not.
Add a new flag cable_connected and set the POWERDOWN flag and
turn off the regulators only if cable is disconnected.

Change-Id: I179db4116d2b5b271916ea4e97534a5cd36fb0a1
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>