USB: gadget: support for dynamic read of usb composition

This change is used to pick one of the pid from
command line parameter and boot the gadget as
per the usb composition.

Change-Id: Ia49b8fd8431675a9fcbf7e7818650d9226fe8685
Signed-off-by: Aniket Randive <arandive@codeaurora.org>