This makes select.poll() interface fully compatible with CpYthon. Also, make
their numeric values of these options compatible with Linux (and by extension,
with iBCS2 standard, which jopefully means compatibility with other Unices too).
py/mphal.h contains declarations for generic mp_hal_XXX functions, such
as stdio and delay/ticks, which ports should provide definitions for. A
port will also provide mphalport.h with further HAL declarations.
Remove include of stm32f4xx_hal.h, replace by include of MICROPY_HAL_H
where needed, and make it compile without float support. This makes
these 3 modules much more generic and usable by other ports.
