stm32: Fix LPUART init failure with low baudrate.

[yn386]

Summary

UART prescaler value should set up collectly to initialize LPUART with low baudrate for STM32G0/G4/H5.
This can be implemented similarly to STM32H7/N6/WB.

The following code does not work:

from machine import UART
uart = UART('LP1', baudrate=9600, bits=8, parity=None, stop=1)

An error occured with following message:

ValueError: set baudrate 0 is not within 5% of desired value

LPUART should be initialized without errors.

Testing

Tested with:

• NUCLEO-G01RB
• NUCLEO-G474RE
• NUCLEO-H563ZI

Remarks

STM32WL may have same issue but I couldn't check because I don't have it.

[github-actions]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:    +0 +0.000% RPI_PICO_W
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS
  qemu rv32:    +0 +0.000% VIRT_RV32

[dpgeorge]

Looks good, thanks!