soc: nxp: kinetis: Add SoC support for k32lx platforms.

Adding supporting soc files for the k32lx platforms and updating
soc.yaml.

Signed-off-by: Ishraq Ibne Ashraf <ishraq.i.ashraf@gmail.com>

soc: nxp: kinetis: k32lx: Use device tree provided value

This clock frequency value will be defined in the board device tree.

Signed-off-by: Ishraq Ibne Ashraf <ishraq.i.ashraf@gmail.com>