According to NXP material, there are no 100 MHz K22F parts in 144 pin
packages, which is the reference manual that this header is supposed to
correspond to.
The header was originally included from Keil uVision Kinetis support
packages. It is possible that this header was only used with
engineering samples of the K22F.
Unify cpu_init for all Kinetis CPUs to reduce code duplication.
Updated the MCG driver implementation to make the configuration easier.
Most clock settings are initialized by kinetis_mcg_init() called from
cpu_init. Board specific external clock source initialization
(FRDM-K64F, PhyNode) needs to be performed in board_init instead of
in cpu_init.
