USB: phy: qusb: Add support for connect/disconnect in QUSB2 PHY

Implement the set_suspend function in the QUSB driver.
This will let the controller driver to allow the PHY
to enter and exit low power mode for scenarios such
as cable connect/disconnect and suspend/resume.

Change-Id: I8a47cf8b2f35d47f86804f42063d6672f5e3b7c7
Signed-off-by: Mayank Rana <mrana@codeaurora.org>