perf machine: Adopt findnew_kernel method

perf machine: Adopt findnew_kernel method

It never was a 'struct dso' method, so fix that by rename
dso__kernel_findnew() to machine__findnew_kernel().

At some point I'll move it all to the machine.[ch] files, for now
lets ease patch review by not moving too much stuff.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-zrxmblgsg5vx0iv4rhvq2f6l@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>