In mboot, the ability to override the USB vendor/product id's was added
back in 5688c9ba09ea8f9ffeeb25bd577a08b57828ffa7. However, when the main
firmware is turned into a DFU file the default VID/PID are used there.
pydfu.py doesn't care about this but dfu-util does and prevents its use
when the VID/PID don't match.
This commit exposes BOOTLOADER_DFU_USB_VID/PID as make variables, for use
on either command line or mpconfigboard.mk, to set VID/PID in both mboot
and DFU files.
8ee2e1fdbc