New ARM armv7a kernels and .S file support in Makefile

Field,

(Just trying out the Pull Request functionality).

This request has two main modifications:

 1. Added a new config folder with the configuration files and micro-kernels from Werner Saar, named armv7a. We still need to discuss if this should replace the old cortex-a9 and cortex-a15 configs, as I am not seeing yet evindent improvements in S/D kernels. These configuration includes, though, tuned kernels for C/Z.

 2. Modified main Makefile in order to consider .S assembly files in the kernels folder. Note I'm not proposing this to replace the old Makefile, but to make you consider an elegant solution (better than mine) to support adding assembly micro-kernels in the framework.

Fran