images: add google-nyan devices

I'm moving these to community in pmaports!4925, but these would be good candidates for prebuilt images even without community category because these devices are fully supported except GPU, so I think there is no need to wait for merging into community category.

wiki:

• https://wiki.postmarketos.org/wiki/Acer_Chromebook_13_CB5-311\_(google-nyan-big)
• https://wiki.postmarketos.org/wiki/HP_Chromebook_14_G3\_(google-nyan-blaze)