[gitlab] Renamed issue labels for target architecture

[Richard Henderson]

I've renamed arch:* to target:* as there was some amount of confusion as to what "arch" 
really meant without context.  I've removed labels for lm32 and unicore32 which have been 
removed from qemu 6.1.  I've added a label for hexagon.

I have not yet added labels for host architecture, because I couldn't figure out how best 
to word the description, or even if all of the target:* labels need re-wording to 
emphasize target.

And then there's the special case of TCI.

Thoughts on these?


r~