Rename of the u-boot-atmel custodian tree

[<Eugen.Hristev@microchip.com>]

Hello everyone,

I plan to rename the u-boot-atmel tree to u-boot-at91 .

It's been more than 5 years since Atmel is part of Microchip, and the 
name is slowly being changed to reflect the new reality.

It makes more sense to have the custodian tree named u-boot-at91 , as 
this tree is used only for patches related to the at91 boards and 
drivers (not any other former Atmel product, nor any other Microchip 
product ). I won't be naming it u-boot-microchip since Microchip does 
much more than just the former Atmel MPUs (AT91 architecture) .

This means, however, that all remotes to this tree have to be updated.
I do not see any other side effect at this moment.

I will wait some more time , few weeks or one month, before making this 
change, to allow anyone to comment on this.

Thanks,
Eugen