r8152: add pre_reset and post_reset

Add rtl8152_pre_reset() and rtl8152_post_reset() which are used when
calling usb_reset_device(). The two functions could reduce the time
of reset when calling usb_reset_device() after probe().

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>