drivers: usb: host: Add set_host_mode

ehci_setup was failing due to async reset sequence that wasn't
completing correctly. It looks like we need to setup the controller
to host mode, before ehci_setup and consequently the async
reset happens.

Change-Id: Ic684af1d10016f6c81934beeb49abd3d30fc7c47
Signed-off-by: Lena Salman <esalman@codeaurora.org>