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.
Lucas De Marchi
Gustavo Jose de Sousa
Andrew Tridgell
Staroselskii Georgii
Jonathan Challinger
Víctor Mayoral Vilches
Víctor Mayoral Vilches