Tell 32-bit users why Tails cannot start

Once we have #8183 (closed), some computers won’t be able to start Tails anymore. We could use syslinux’ ifcpu64 module or similar to display a message explaining them what’s happening. This would decrease the load on our frontdesk, and be nicer to these users.

Feature Branch: feature/8183-64bit-userspace

Related issues

Related to #8183 (closed)
Blocks #12431 (closed)
Blocks #11997 (closed)

Original created by @intrigeri on 11638 (Redmine)

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