Zephyr renamed CONFIG_FLOAT to CONFIG_FPU to better reflect its semantics
of enabling the hardware floating point unit (FPU) rather than enabling
toolchain-level floating point support (i.e., software floating point for
FPU-less socs).
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.