USB: phy-msm-usb: Resume root hub on receiving ASYNC interrupt

An ASYNC interrupt is an indication by hardware that some
activity has happened on USB lines in LPM (low power mode)
and USB software should now bring it out of LPM.
Ideally, hardware should give one more interrupt after coming
out of LPM (turning clocks ON) so that USB driver can process
that accordingly. But, sometimes this interrupt is not generated
from h/w for remote wakeup event in host mode. Hence, resume root
hub on receiving the ASYNC interrut from hardware only in Host mode.
This also helps to put USB in LPM on receiving any spurious async
interrupt.

CRs-fixed: 650233
Change-Id: I82a67c061e167e3531a17ca12e082bd20a3b61e1
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>