sama5d3_xplained: change machine definition due to illegal character

Because of the "_" in the former sama5d3_xplained machine name, we had this
error while building the SDK:
DEBUG: Executing python function do_package_ipk
meta-environment-sama5d3_xplained
*** Error: Package name contains illegal characters, (other than [a-z0-9.+-])

This error is due to presence of uppercase, space or underscore or any other
characters other than [a-z0-9.+-] in MACHINE definition.
So we move to "-" for this machine definition.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
atmel-demo-image: switch to function for removal of kernel images

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
meta-atmel: Modify internal variables

Conforming to OE/Yocto naming convention, the layer should not use the
meta prefix for BBFILE_COLLECTIONS and other layer-specific variables.

Signed-off-by: David Vincent <freesilicon@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
README: provide clearer information about meta-atmel layer

Add information about the meta-atmel layer in a more readable way. It also
conforms to the typical README file of Yocto layers with:
- supported machines
- source code location
- the way to contribute to this layer (mailing-list, maintainers)

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
at91bootstrap: 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.

Simplify deployment of at91bootstrap images by creating symlinks to the
final image. The deployment directory is also populated with symlinks to
point to the last generated image.

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>
[nicolas.ferre@atmel.com: adapt to newer revision and modify a little bit]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
at91bootstrap: Add development recipe

To follow the development of at91bootstrap and generate images based on
the latest revision, create a new recipe following Yocto Project
versioning guidelines : http://openembedded.org/wiki/Versioning_Policy

Signed-off-by: David Vincent <freesilicon@gmail.com>
[nicolas.ferre@atmel.com: adapt to newer recipies, add weak priority]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
at91bootstrap: Keep only latest recipe used by all boards

All available boards in meta-atmel are supported by the latest at91bootstrap
recipe (3.7).
So, keep only one recipe as recommended by the Yocto project :
https://wiki.yoctoproject.org/wiki/Best_Known_Methods_(BKMs)_for_Package_Updating

Reported-by: David Vincent <freesilicon@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>