LPC31 and SAMA5Dx EHCI drivers: Fix cache related problem. All buffers are...

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.