usb: gadget: Draw 900mA current when enumerating in super speed mode

Currently 500mA is used as max allowable current to draw with USB SDP
case in both super speed and high speed mode. In super speed mode it
is allowed to draw 900mA current. Hence update allowable current to
draw based on USB connection speed. This change doesn't consider any
configuration based allowable max current.

Change-Id: Iae9ecf586135b0a2064e7d5e6e8fa3d8e7e4fb70
Signed-off-by: Mayank Rana <mrana@codeaurora.org>