perf test: Enable Symbols test to work with a current module dso

The test needs a struct machine and creates one for the current host,
but a side-effect is that struct machine has set up kernel maps
including module maps.

If the 'Symbols' test --dso option specifies a current kernel module,
it will already be present as a kernel dso, and a map with kmaps needs
to be used otherwise there will be a segfault - see below.

For that case, find the existing map and use that. In that case also,
the dso is split by section into multiple dsos, so test those dsos
also. That in turn, shows up that those dsos have not had overlapping
symbols removed, so the test fails.

Example:

  Before:

    $ perf test -F -v Symbols --dso /lib/modules/$(uname -r)/kernel/arch/x86/kvm/kvm-intel.ko
     70: Symbols                                                         :
    --- start ---
    Testing /lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko
    Segmentation fault (core dumped)

  After:

    $ perf test -F -v Symbols --dso /lib/modules/$(uname -r)/kernel/arch/x86/kvm/kvm-intel.ko
     70: Symbols                                                         :
    --- start ---
    Testing /lib/modules/6.7.2-local/kernel/arch/x86/kvm/kvm-intel.ko
    Overlapping symbols:
     41d30-41fbb l vmx_init
     41d30-41fbb g init_module
    ---- end ----
    Symbols: FAILED!

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240131192416.16387-1-adrian.hunter@intel.com