usb: core: Reduce resume signalling time for devices behind external hub

Squashing commit 28f110a27130("usb: core: Add support to skip
extended bus resume delay") and e97aab2199f3("usb: core: Drive resume
for 20ms for devices behind external hub") with few modifications.

This change removes extra 40ms delay upon bus resume for the
exteral hub and reduce the resume signalling time from 40ms to
20ms for devices behind the external hub(s). Skipping extra
delay reduces over all bus resume latency.

Change-Id: I948626bbaae0c78553543347a1c7d5b8168c08cd
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>