soc: nxp: Flatten MCX SOCs

Turn MCX series into families.

Reasoning:
 1. The MCX SOCs are quite different from each other and having them all
    under one family in the HWMv2 hierarchy is fruitless because there
    are so many differences that it is confusing to try to introduce
    family-level code and configs since they would each only apply to a
    subset of the series. There is almost nothing that can be shared
    between all of them. Which is why there are comments in the MCX
    family files saying not to put anything in them. This is a technical
    waste.
 2. Therefore, turning all of them into families is almost 0 effort and
    makes sense. It will allow these different types of MCX to be
    further subdivided into series in the future as the MCX portfolio
    expands and such division will be necessary as new SOCs within each
    letter family are released.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>