usb: gadget: f_gsi: Fix function suspend

The func_is_suspended and func_wakeup_allowed flags are now not
part of the struct usb_function; hence move those fields to the
local struct f_gsi. Guard the get_status() callback within
CONFIG_USB_FUNC_WAKEUP_SUPPORTED as it should return 0 if
function wakeup is not supported. Finally fix up various usage
of the FUNC_SUSPEND flags to use the standard definitions found
in <uapi/linux/usb/ch9.h>.

Change-Id: If206b8ed82a69041fff70e244a116109ef5e5aaf
Signed-off-by: Jack Pham <jackp@codeaurora.org>