SAMA5D OHCI: Remove a local variable that is unused when debug is disabled; refresh a configuration.  Update a README

Update some READMEs.  For all implementation of the USBHOST waiter, make sure that the waiter thread stack size is larger if the USB hub feature is enabled

Olimex LPC1766STK: The USB host waiter stack should be configurable because it needs to be a lot depending when using a hub

LPC31 and SAMA5Dx EHCI drivers: Fix cache related problem.  All buffers are now aligned with the cache line size in both starting address and in length.  This cause major problems in unlucky builds where the USB host buffers where unaligned and abbutting other data.  The cache flush and invalidate operations could be subverted by acceses to adjacent data or could have unexpected side effects.  This bug has been in the ECHI drivers forever, but was only revealed due to unlucky memory allocations during the integration of the hub feature.

USB host: If the implementation of the disconnect method frees the EP0 endpoint, then it must nullify it in the port structure

STM32 USB device.  Add protection in the event that out-of-bound enpoint numbers are received.  From David Sidrane.

USB host:  Need to include the port structure when disconnecting, otherwise may destroy a root hub port

LPC17 GPIO:  Reorder steps when an output GPIO is configured in order to avoid transient bad values from being output.  From Hal Glenn.

SAM PIO: sam_pio.h needs to include chip/sam_memorymap.h in order to resolve some conditional logic properly

Added missing EXTI definitions for the STM32 F3; Correct an error the port D base address in the STM32 F3 and F37 memory maps.  From Greg Meiste.

STM32F4-Discovery: Part of logic to initialize the ELF loaded in the board startup logic.  From Leo aloe3132