MPU9250 Reset reorganization (fixes I2C functionality)

[dennisss]

During MPU9250 initialization, depending on passthrough modes, the main chip must be reset() before the magnetometer connection is initialized in order to setup the passthrough to the magnetometer.

Current sequence of events (during init):

...

• reset()
  • "MPU6050" reset
  • AK8963 reset <- fails because not yet connected
• Magnetometer init/connect

...

Fixed sequence:

...

• reset_mpu()
  • "MPU6050" reset
• magnetometer init
• ak8963_reset()
  • AK8963 reset

...

The functionality of reset() is preserved, but for the initialization phase, the reset is split into a two phase reset.

Fixes #7624

Also adds a one liner fix specified in another issue report.

[davids5]

@dennisss

I am assuming the mpu9250 is connected by I2C.
I am sorry this was not tested, and your fix makes total sense. Thank you!

I would like to see the the SPI->I2C code moved to an interface and not have all this if pass through, but just invoke the functions on the interface.

[davids5]

Jenkins test this please.

[davids5]

@dennisss

What HW are you testing on? I have a few more changes to make and I would like to test the I2C interfaces as you were.

[dennisss]

@davids5 the only platform I know of that does this is the Crazyflie 2 which is what I'm testing on.

Feel free to mention me in any PR's that may effect this so that I can test them.

And, yes it is connected via I2C, with the magnetometer as well as another sensor all setup to share the I2C bus provided by the MPU.