MBA 2017 won't boot up in macOS, but will in Ubuntu
While the "Unsupported CPU" and "Unsupported PCH" messages in the log appear concerning, I wouldn't jump to the conclusion that this is what's causing the problem. The fact is I've seen these messages before in Macs that run perfectly fine.

I see you've already reset the SMC, but you haven't mentioned resetting the NVRAM and this is something you should also do.

Reset your NVRAM

For your model MBA you'll need to follow these steps:


Fully shut down your MBA 
Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
Hold those keys down until your Mac reboots again (i.e. wait until you've heard the startup chime a second time)
Let go of the keys and let your MBA reboot. 


It's not clear to me if you still have macOS installed or not:


If not, then shut down your Mac again and switch it on and immediately press the option key and let me know what drive options (if any) appear on the screen.
If so, what happens when your MBA boots up after the NVRAM reset?