usb: gadget: Disable USB2 LPM Support

USB device is failing to initiate L1 remote wakeup for following
scenarios:-

1) When USB host initiates L1 between control transfers
(Setup and Status Phase).
2)In case of BULK only composition when USB host initiates L1 after
PING retries on OUT endpoint. Device fails to initiate L1 remote
wakeup when SW issues start transfer.
3) When bus is suspended and Start transfer is issued on IN TRB

Hence disable high speed link power management support by advertising
bcdUSB as 2.0 in high speed mode.

Change-Id: I83124d5e3821ba979be4772bc04e41f05dc7492c
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>