usb/xhci: Change how we indicate a host supports Link PM.

usb/xhci: Change how we indicate a host supports Link PM.

The xHCI driver currently uses a USB core internal field,
udev->lpm_capable, to indicate the xHCI driver knows how to calculate
the LPM timeout values.  If this value is set for the host controller
udev, it means Link PM can be enabled for child devices under that host.

Change the code so the xHCI driver isn't mucking with USB core internal
fields.  Instead, indicate the xHCI driver doesn't support Link PM on
this host by clearing the U1 and U2 exit latencies in the roothub
SuperSpeed Extended Capabilities BOS descriptor.

The code to check for the roothub setting U1 and U2 exit latencies to
zero will also disable LPM for external devices that do that same.  This
was already effectively done with commit
ae8963adb4ad8c5f2a89ca1d99fb7bb721e7599f "usb: Don't enable LPM if the
exit latency is zero."  Leave that code in place, so that if a device
sets one exit latency value to zero, but the other is set to a valid
value, LPM is only enabled for the U1 or U2 state that had the valid
value.  This is the same behavior the code had before.

Also, change messages about missing Link PM information from warning
level to info level.  Only print a warning about the first device that
doesn't support LPM, to avoid log spam.  Further, cleanup some
unnecessary line breaks to help people to grep for the error messages.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Alan Stern <stern@rowland.harvard.edu>