audiodev: Add support for amplifiers without current feedback

Introduce very simplistic motor modeling by assuming some arbitrary
attenuation at higher frequencies. This will be compensated by just
lowering the output gain at DC.

Signed-off-by: David Jander <djander@gmail.com>
config: Reduce maximum feedrate slightly

The feedrate is high enough anyway. This permits reducing Z current a
little

Signed-off-by: David Jander <djander@gmail.com>
grunner.conf: Order config options

Signed-off-by: David Jander <djander@gmail.com>
temp100: Correct scaling factors for new hardware version

Signed-off-by: David Jander <djander@gmail.com>
grunner: Optimize use of self.cfg instead of creating new instances

Signed-off-by: David Jander <djander@gmail.com>