tegra: move common features to a common makefile

tegra: move common features to a common makefile

For Non-Nvidia boards to include newly added features (like emc clock
scaling) it would be necessary to add each feature to their own board
Makefile. This is because currently the top Makefile automaticly includes
these features only for Nvidia boards.

This patch adds a simple Makefile include so all new features become
available for non-Nvidia board vendors.

Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Tom Warren <twarren@nvidia.com>
Cc: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>