perf data: Add global path holder

Add a 'path' member to 'struct perf_data'. It will keep the configured
path for the data (const char *). The path in struct perf_data_file is
now dynamically allocated (duped) from it.

This scheme is useful/used in following patches where struct
perf_data::path holds the 'configure' directory path and struct
perf_data_file::path holds the allocated path for specific files.

Also it actually makes the code little simpler.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20190221094145.9151-3-jolsa@kernel.org


[ Fixup data-convert-bt.c missing conversion ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>