xhci: Don't enable/disable RWE on bus suspend/resume.

The RWE bit of the USB 2.0 PORTPMSC register is supposed to enable
remote wakeup for devices in the lower power link state L1.  It has
nothing to do with the device suspend remote wakeup from L2.  The RWE
bit is designed to be set once (when USB 2.0 LPM is enabled for the
port) and cleared only when USB 2.0 LPM is disabled for the port.

The xHCI bus suspend method was setting the RWE bit erroneously, and the
bus resume method was clearing it.  The xHCI 1.0 specification with
errata up to Aug 12, 2012 says in section 4.23.5.1.1.1 "Hardware
Controlled LPM":

"While Hardware USB2 LPM is enabled, software shall not modify the
HIRDBESL or RWE fields of the USB2 PORTPMSC register..."

If we have previously enabled USB 2.0 LPM for a device, that means when
the USB 2.0 bus is resumed, we violate the xHCI specification by
clearing RWE.  It also means that after a bus resume, the host would
think remote wakeup is disabled from L1 for ports with USB 2.0 Link PM
enabled, which is not what we want.

This patch should be backported to kernels as old as 3.2, that
contain the commit 65580b43

 "xHCI: set
USB2 hardware LPM".  That was the first kernel that supported USB 2.0
Link PM.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@vger.kernel.org