usb: dwc3: gadget: Set BESL config parameter

When operating with LPM signals, the controller asserts the deep
low-power signal (utmi_l1_suspend_n) to the phy when the BESL value of
the LPM token is equal to or greater than DCTL.HIRD_Thres[3:0] (and
with DCTL.HIRD_Thres[4] set). Otherwise, the shallow low-power signal
(utmi_sleep_n) is asserted. Set the recommended deep BESL equal to the
controller's DCTL.HIRD_Thres[3:0] setting, and set the baseline BESL
to 0 for the shallow low-power signal. This maximizes the opportunity
for L1 residency and optimizes power savings.

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>