ec: Replace fan interpolation/smoothing with fixed step

This change is made separately from the previous commit as it is a
significant change in behavior that affects all laptops. Copying the
message from the EC commit:

> Fan noise is one of the top complaints reported. The existing
> interpolation and smoothing logic has not sufficiently addressed the
> issues with fans changing speeds too quickly in response to rapid
> changes in thermals (particularly from PECI).
>
> This behavior can be observed by with very basic tasks, such as:
>
> - Powering on a system and logging into GNOME
> - Starting a GUI application such as Firefox
>
> Replace them with a fixed step update per event interval. Fans now have
> a maximum amount they change change over time (3.9%/sec) as they move
> towards a target duty.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

CHANGELOG.md

@@ -18,6 +18,8 @@ features apply to your model and firmware version, see the
 - Changed fans to use highest reported temperature to calculate duty instead
   of using the highest calculated duty across all fans
 - bonw15-b: Added initial release of open firmware with System76 EC
+- Changed fan mechanism from calculated interpolation/smoothing to a fixed
+  step to limit rapid changes in duty over short periods
 
 ## 2024-07-08
 

ec

@@ -1 +1 @@
-Subproject commit 88ad52491a40e56c97ca0a595b36cb3f1629198c
+Subproject commit 3d8204c3f40b4de1e3b94f2c1aaca5f29a80122e