Use common EZSP init

[agners]

This allows to use bellows CLI command with zigbeed.

[codecov-commenter]

Codecov Report

Merging #488 (37070b5) into dev (0b297b0) will decrease coverage by 0.06%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##              dev     #488      +/-   ##
==========================================
- Coverage   99.92%   99.86%   -0.07%     
==========================================
  Files          51       51              
  Lines        4283     4290       +7     
==========================================
+ Hits         4280     4284       +4     
- Misses          3        6       +3     

Impacted Files	Coverage Δ
bellows/ezsp/__init__.py	97.34% <83.33%> (-1.29%)	⬇️

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[agners]

Closing as this is handled by #487.