When compiled with hard float the system should enable FP access when it
starts or else FP instructions lead to a fault. But this minimal port does
not enable (or use) FP and so, to keep it minimal, switch to use soft
floating point. (This became an issue due to the recent commit
34c04d2319 which saves/restores FP registers
in the NLR state.)
These ports don't need anything from extmod so don't include those files
at all in the build. This speeds up the build by about 10% when building
with a single core.
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.
