Improve CPU throttle lines in TinyPilot logs (#1543)

Resolves #1489

Parses the output of `vcgencmd get_throttled` into a simple “yes” or
“no” result.

## Decoding the output of `vcgencmd get_throttled`

We could decode the output of `vcgencmd get_throttled` to get more
details, but for our purposes we simply want to detect that nothing
relating to throttling has occurred since the device was booted, a
situation which is indicated by an output value of `0x0`.
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debian-pkg/opt/tinypilot-privileged/scripts/collect-debug-logs

@@ -136,7 +136,15 @@ print_info "Checking temperature..."
 } >> "${LOG_FILE}"
 
 print_info "Checking throttled state..."
-printf "%s\n\n" "$(vcgencmd get_throttled)" >> "${LOG_FILE}"
+{
+  CPU_THROTTLED="yes"
+  if vcgencmd get_throttled | grep --line-regexp --quiet "throttled=0x0" ; then
+    CPU_THROTTLED="no"
+  fi
+  readonly CPU_THROTTLED
+  echo "CPU throttled since boot: ${CPU_THROTTLED}"
+  printf "\n"
+} >> "${LOG_FILE}"
 
 print_info "Checking for voltage issues..."
 {