perf disasm: Define stubs for the LLVM and capstone disassemblers

perf disasm: Define stubs for the LLVM and capstone disassemblers

This reduces the number of ifdefs in the main symbol__disassemble()
method and paves the way for allowing the user to configure the
disassemblers of preference.

Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Aditya Bodkhe <Aditya.Bodkhe1@ibm.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Link: https://lore.kernel.org/r/20241111151734.1018476-3-acme@kernel.org
[ Applied fixes from Masami Hiramatsu and Aditya Bodkhe for when capstone devel files are not available ]
Link: https://lore.kernel.org/r/B78FB6DF-24E9-4A3C-91C9-535765EC0E2A@ibm.com
Link: https://lore.kernel.org/r/173145729034.2747044.453926054000880254.stgit@mhiramat.roam.corp.google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>