dwc3-msm: Do not resume usb3 phy if max speed is HS only

usb3 phy is needed when core is operating at super speed or
higher. Do not turn on usb3 phy clocks even when core is
programmed to work at high speed only mode. While at it,
remove redundant module parameter to control max speed. Speed
can be controlled using existing sysfs entry.

Example: To set High speed only:
echo "high" > /sys/devices/platform/soc/<devname>/speed

To set super speed:
echo "super" > /sys/devices/platform/soc/<devname>/speed

Change-Id: I24a9a869d97e6efc3ebc0d7a1374805139c65648
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>