AMDGPU: Teach disassembler to produce target id directives (#203979)

Inspect the binary's e_flags to reproduce the .amdgcn_target directive.
This is a step towards round-trip disassembly without depending
on command line state specifying the subtarget. I wasn't sure
where to put the emission to ensure it is always emitted. I
also do not know why it's OK to just write to outs(), but that's
what the other directives here were doing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
GitOrigin-RevId: 1915af8a196863d604eb1c58cf99e64a0ec58153