[WIP] Baud autodetect

[andreagilardoni]

This PR aims to implement an autodetect for UART, so that it is possible to change the baudrate from renesas mcu.
This PR is the continuation on the discussion performed here: #56
Missing features

• detect when the baudrate needs to be changed
  - discover it by adding a CRC, ECC or whatever (open to discussion)
  - discover by the size of the incoming message
  - others
• Fix E (5553) uart: uart_get_buffered_data_len(1342): uart driver error
• code cleaning
• retro compatibility with previous version of FW

[andreagilardoni]

Hi @matthieuvigne and @JAndrassy, I am trying to implement via FW the baudrate autodetect feature.
My Idea is the following:

• the board boots up, autodetect starts on esp, looking for character 0x55
• The renesas MCU calls begin on modem, with either the default value or a custom one.
• the esp gets the correct value, sends 0x55 back and starts correctly

if an error occurs on Renesas and the MCU is reset, then:

• the renesas restarts the baudrate autodetection procedure
• esp needs to discover that something has happened and restart the detection [missing]

if an error occurs on ESP and the MCU is reset, then:

• the renesas core needs to detect the fault [missing]
• renesas core restarts the autodetect procedure