Replace loading splash with missing fbcon warning when booting into installation with UI=fbkeyboard

Describe your issue

The fbkeyboard UI depends on framebuffer console (fbcon) support in the kernel to function. When missing, the "Loading..." splash sticks.

What's the expected behaviour?

The loading splash should be replaced with a clear explaination to why there isn't a login console visible.

What's the current behaviour?

The "Loading..." splash sticks.

How to reproduce your issue?

For example when booting into samsung-kylepro with UI fbkeyboard.

What device are you using?

samsung-kylepro

On what postmarketOS version did you encounter the issue?

• edge (master branch)
• v21.06
• v21.03 (supported until 2021-08-04)

On what environment did you encounter the issue?

Phone environments

• Phosh
• Plasma Mobile
• Sxmo

Other

• No environment
• GNOME
• KDE Plasma
• Kodi
• MATE
• Shelli
• Sway
• Weston
• Xfce4
• fbkeyboard
• i3wm

How did you get postmarketOS image?

• from https://images.postmarketos.org
• I built it using pmbootstrap
• It was preinstalled on my device

What's the build date of the image? (in yyyy-mm-dd format)

2021-07-19

Additional information