Widget: Primary Flight Display acts as a CPU hog after telemetry data

Go straight to https://github.com/ArduPilot/apm_planner/issues/646#issuecomment-221203527 for best info about how to reproduce

APM planner takes about 30% CPU time on a quad core 2.4Ghz laptop ftom the moment of serial connection. Reproducible on Intel graphics only, yet it's the apmplanner2 process that hogs CPU, not some drivers.
Disconnecting makes it drop less then 5% , to about 26%
This goes also for non-graphic views whithout maps/AHI

Please provide info on how to use gdb or other tools to report better if needed.

Start with the reproduction details in issue comment 221203527 and profile apmplanner2 from serial connection through telemetry updates, focusing on the Primary Flight Display widget. Use gdb or another profiler as suggested; done means identifying and correcting the post-telemetry CPU increase and confirming CPU usage drops without disconnecting or changing views.

Written by the indexing model from the issue text.