These are not used. The only place where raw fields are used are in the
compass calibrator and we don't need to store them.
Additionally remove duplicated documentation about the meaning of the
functions to avoid them getting out of sync.
the previous approach assumed a 1:1 mapping between compass backends
and compass instances, which isn't true on PX4.
It also only setup milligauss offsets on a set_and_save call, which is
not the only way offsets change
this adds a milligauss_ratio per instance, which is considerably
simpler
From now on there's a pair get_field_milligauss() and
get_offsets_milligauss() that can make the transition to the common
units across all compasses easier.
_copy_to_frontend function takes care of abstracting
this code from the driver. For now the function takes
care of the offset and rotation that is common.
Gustavo Jose de Sousa
Andrew Tridgell
Lucas De Marchi
Staroselskii Georgii
Jonathan Challinger
Víctor Mayoral Vilches
Víctor Mayoral Vilches