Also move MICROPY_PY_PENDSV_ENTER/REENTER/EXIT to mphalport.h, for ports
where these are not already there.
This helps separate the hardware implementation of these macros from the
MicroPython configuration (eg for renesas-ra and stm32, the IRQ static
inline helper functions can now be moved to irq.h).
Signed-off-by: Damien George <damien@micropython.org>
API change: time.time_ns() is added, but it just returns 0.
No API or functional change to existing time functions.
Signed-off-by: Damien George <damien@micropython.org>
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.