usb: ehci_msm2: Resume root hub on receiving ASYNC interrupt

An ASYNC interrupt is an indication by hardware that some
activity has happended 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 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 interrupt from hardware in Host mode.

CRs-Fixed: 369298
CRs-Fixed: 368948
Change-Id: Ifb166c1f3c749ab8c615308ab52d85ccdc666733
Signed-off-by: Chiranjeevi Velempati <cvelempa@codeaurora.org>