Some periph_rtt implementations do not provide `rtt_set_counter()`. This
adds `periph_rtt_set_counter` as feature to allow testing for its
availability. The feature is provided at CPU level if periph_rtt is
provided by the board for all CPUs implementing `rtt_set_counter()`.
MCG_Lite is used in many KL parts and is a less advanced clock generator
than the full MCG used in the K series. This change lets the MCG_Lite
and MCG share the same user facing API, with some configuration
differences.
Now that CPU and CPU_MODEL are defined in the board's Makefile.features
it can be used to determine the available features provided by the
specific model.
This removes doing `filter-out periph_hwrng, $(FEATURES_PROVIDED)`
after processing `cpu/$(CPU)/Makefile.features`.
The current solution is a HACK as `CPU_MODEL` is currently not available
at that moment but will be in the near future.
It will allow always including `cpu/$(CPU)/Makefile.features` after
`boards/$(BOARD)/Makefile.features`.
It is a part of moving `CPU/CPU_MODEL` definitions to `Makefile.features`.
