sama5d3xek: Take into account the Android kernel bootarg config option

For Android, the kernel bootarg config was hardcoded in the sources. This
patch changes this to take into account the config set during configuration
step.

Signed-off-by: Yann Soubeyrand <ysoubeyrand@adeneo-embedded.com>
Merge pull request #12 from yann-soubeyrand/master

sama5d3xek: Take into account the Android kernel bootarg config option