STM32F4-Discovery: Add configuration option to select the size of the stack used with the usbhost waiter.  Needs to be bigger when a hub is supported

USB HUB: Fix a deadlock that can occur if the HCD and the HUB try to share the high priority work queue.  Now how work must be done on the low priority work queue.

USB HUB: Update all USB host connection waiter application threads to use the the new connection interface

STM32 PVD: Adds support for STM32's Programmable Voltage Detector feature. I put register access behind CONFIG_STM32_ENERGYLITE as have not checked F1/F2/F4 etc. manuals. Tested on STM32L1. PVD interrupt looks generic, at least #defines it needs are in headers for every chip variant.  By Dmitry Nikolaev, submitted by Juha Niskanen.

Networking: If IPV6 is not enabled, an warning occurs for an unused variable, which is currently used inside the IPV6 block, but declared outside.  From ObitalFox.

ECHI HCDs: Separate logic used in synchronous transfers so that it can be used in forthcoming asynchronous transfer

Port hub support to LPC31 from SAMA5; Updated Olimex-LPC-H3131 for hub support and refresh configurations