[Buildroot] [RFC] Firmware handling in BR

[yegorslists at googlemail.com]

So I made the first attempt to add binary firmware images to BR. I placed the stuff under "Hardware handling" in the configuration menu, but I think it would be better to place this menu direct under "Package selection for the target".

Some more issues:

1. at the time firmware script creates /lib/firmware folder itself: should it be included in skeleton?
2. /lib/firmware will be used by firmware package and by udev at build/config time: should we introduce a env variable for this?

Regards,
Yegor