usb: phy: qmp: Clear rx path during link training in Gen2 mode

commit 51ba5b1e ("usb: dwc3: Notify super speed phy
about link training") enabled software procedure to clear rx
path during link training to avoid compatibility issues with
SSP (super speed plus) capable hosts. On newer hardware
revisions, clearing rx path can be enabled in phy itself.

Change-Id: Ifcfc33d93a222697cdbdddcc73ce28f7503d1a7d
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>