Create common recipe file

Create an include file for at91bootstrap recipe to have a common
configuration for all versions. This way, releasing a new version should
only result in a new recipe with an updated SRC_URI.

Also, keep only one recipe as recommended by the Yocto project :
https://wiki.yoctoproject.org/wiki/Best_Known_Methods_(BKMs)_for_Package_Updating

Signed-off-by: David Vincent <freesilicon@gmail.com>