objtool: Print headers for alternatives

objtool: Print headers for alternatives

When using the --disas option, objtool doesn't currently disassemble
any alternative. Print an header for each alternative. This identifies
places where alternatives are present but alternative code is still
not disassembled at the moment.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-20-alexandre.chartre@oracle.com