encoder_as5047: Add SPI loose magnet detection logic

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This code is meant to fix situations where the magnet gets loose and causes the motor to rotate very fast. The solution is for encoders of type AS5047 and it compares the FOC observer phase against the physical encoder phase at high speeds and if they are not in sync than a loose magnet fault is displayed and the motor will stop.
vedderb/vesc_tool#453

[vedderb]

This is an interesting and useful addition, but there are a few things I would like to change:

• There should be some way to disable it as you can have motors where the observer does not track well at all under heavy load even at high speed.
• All encoder have a chance of slipping, so this should really be used on all encoders when enabled. Some extra care probably has to be taken for encoders that use an index-pulse.

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Hi,
Thank you for your feedback!
Before I add the changes you suggested, do you have a preference where I should add this options in the Vesc tool?