usb: dwc2: Fix HiKey regression caused by power_down feature

usb: dwc2: Fix HiKey regression caused by power_down feature

In 4.17-rc, commit 03ea6d6e9e1f ("usb: dwc2: Enable power down")
caused the HiKey board to not correctly handle switching between
usb-gadget and usb-host mode.

Unplugging the OTG port would result in:
[   42.240973] dwc2 f72c0000.usb: dwc2_restore_host_registers: no host registers to restore
[   42.249066] dwc2 f72c0000.usb: dwc2_host_exit_hibernation: failed to restore host registers

And the USB-host ports would not function.

And plugging in the OTG port, we would see:
[   46.046557] WARNING: CPU: 3 PID: 6 at drivers/usb/dwc2/gadget.c:260 dwc2_hsotg_init_fifo+0x194/0x1a0
[   46.055761] CPU: 3 PID: 6 Comm: kworker/u16:0 Not tainted 4.17.0-rc5-00030-ge67da8c #231
[   46.055767] Hardware name: HiKey Development Board (DT)
[   46.055784] Workqueue: dwc2 dwc2_conn_id_status_change
...

Thus, this patch sets the hisi params to disable the power_down
flag by default, and gets thing working again.

Cc: John Youn <johnyoun@synopsys.com>
Cc: Vardan Mikayelyan <mvardan@synopsys.com>
Cc: Artur Petrosyan <arturp@synopsys.com>
Cc: Grigor Tovmasyan <tovmasya@synopsys.com>
Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: linux-usb@vger.kernel.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>