Reproduction Steps:
1. Create new project
2. Edit > Project Settings > Player
3. Under Icons notice that there is no 2x resolution selection
Note: Apple requires 2x resolution images for 4k TVs
https://developer.apple.com/tvos/human-interface-guidelines/icons-and-images/image-size-and-resolution/

Expected Behaviour: Ability to add 2x images that are required to upload the project to tvOS App Store.
Actual Result: No provided way to add 2x images.

Reproduced on versions: Unity 2017.1.1p2, 2017.2.0f3, 2017.3.0b4

Fixed in 2017.1.3p3, 2017.2.2p3, 2017.3.2f1, 2018.1.0f1, 2018.2.0b1.