Do not enable led sw breathing if current led backend does not support it

This is needed so that mce will not take breathing wakelock and block
suspend in situations where led backend will not be doing breathing.

[mce] Do not enable led sw breathing if current led backend does not support it. Contributes to JB#21845
Merge pull request #199 from spiiroin/can_breathe

Do not enable led sw breathing if current led backend does not support it