Is JMicronATA.kext part of Yosemite? And others
It's the kernel extension for JMicron SATA controllers, and yes it's official, as are the others. It's up to you if you want to delete them, I wouldn't bother as they take up minimal space. Check System Profiler before doing anything silly just to make sure your iMac doesn't require any of the listed extensions.

Example:


  JMicronATA:
  
  Version:    1.1.6
  
  Last Modified:  5/22/12, 8:19 AM
  
  Loaded: No
  
  Get Info String:    1.1.6, Copyright JMicron Technology Corporation
  
  Obtained from:  Not Signed
  
  Kind:   Intel
  
  Architectures:  x86_64
  
  64-Bit (Intel): Yes
  
  Location:   /System/Library/Extensions/JMicronATA.kext
  
  Kext Version:   1.1.6
  
  Valid:  Yes
  
  Authentic:  Yes
  
  Dependencies:   Satisfied
  
  Signed by:  Not Signed