Add Kinetis SoC family and rename fsl_frdm_k64f to mk64f12.
This will allow adding new SoCs of the same family and the reuse of code
among SoCs of the family and series.
Change-Id: Iea1a663aef7ce0487f147bdd36f668bebe80deb5
Signed-off-by: Anas Nashif <anas.nashif@intel.com>