USB: HSIC: Add support for HSIC core and SMSC HUB using DT

Add device tree support in SMSC HUB driver which also registers
platform_device for HSIC as its child. This allows SMSC HUB driver
to turn OFF clocks for power savings after HSIC is suspended.
Also add support for SMSC HUB to use dedicated clock as ref_clk
instead of XO.

Change-Id: I3e8828ddc232936df3e21c8e1158af92b16996a2
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>