Xiaomi Philips brightness (#6091)

[s-hadinger]

Description:

I don't own a Philips Xiaomi bulb, but simulated on a led device. This should be back to 6.5.0 behavior.

Related issue (if applicable): fixes #6091

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core 2.3.0, 2.4.2 and 2.5.2
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.