title: Disable p-dropdown depending selection of another p-dropdown PrimeNG
body: <p>I am using PrimeNG in my angular app, I have issue with p-dropdown</p>
  
  <p><strong>Question</strong></p>
  
  <p>I have two dropdowns for country and caste_category, I provide caste_reservation for only India , in case of other country selection , the OPEN option from caste_category needs to get selected and make the disable that dropdown.</p>