Official Syllabus for GATE 2019 is not out yet. Though, You can prepare as per the 2018 Syllabus since It is less probable that It will change and even if it does change, you can prepare for the extra topics added later.
And as per the GATE 2018 Syllabus is concerned, Horizontal and Vertical Micro programming is there in the syllabus under Control Unit chapter of Computer Organization and Architecture.