Librem EC Enhancements

series of small enhancements:

• enable orange warning LED when battery below 20%
• remove some debugging output
• save user settings to BRAM
• show orange LED when battery critical
• save charge thresholds to BRAM
• reduce power button debouncing to fix S3 resume
• fix power state LED logic
• rework HP detection logic
• Enable Fn-Space to toggle kb backlight