BroadwellDEFspPkgBin USB initialization issues

With Broadwell-DE MR2 FSP, USB port initialization has multiple issues:

- only user-facing controls are to enable/disable the two EHCI controllers; nothing for XHCI
- with SeaBIOS payload, attached USB devices only detected if FSP debug level set to 3 *and* MRC cache disabled (or first boot after flashing)
- with Linux payload, ehci/xhci host controllers (and child devices) only detected when modules compiled with =y (vs =m); attached devices detected but non-functional

edit: USB ports/attached devices are fully functional once Linux kernel has booted regardless of state in bootloader