perf script: Fix script_fetch_insn for more than just x86

perf script: Fix script_fetch_insn for more than just x86

The script_fetch_insn code was only supported on natively running x86.

Implement a crude elf_machine_max_instruction_length function and use to
give an instruction length on more than just x86.

Use the ELF machine to determine the length to use to support
cross-architecture development.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shimin Guo <shimin.guo@skydio.com>
Cc: Yujie Liu <yujie.liu@intel.com>
[ Conditionally define EM_CSKY and EM_LOONGARCH for older distros ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>