Dear buildroot maintainer:
 Since more and more traditional companies are starting using buildroot  with AT91SAMx chipset as their product firmware, much of them are still  using SVN as their version control system. So add svn repository method  to AT91bootstrap3 package.
It's a milestone to me that i from a parasite to a buildroot contributor, if there is any incorrect in this patch, feel free to tell me via email(xiangyu.chen@aol.com).
Thanks!

Br,Xiangyu