Cull Atmel board configs no longer relevant.
Remove most of the Atmel at91 boards. Most of them are no longer
relevant or used by people. Kept ATMEL since it should work on all the
boards that still work (I've not confirmed this, since I don't have
all these boards). Also kept SAM9G20EK, since I have several boards
that it is used on. If I've deleted a kernel in error, please let me
know.