tools/power turbostat: Fix build with musl

tools/power turbostat: Fix build with musl

turbostat.c: In function 'parse_int_file':
    turbostat.c:5567:19: error: 'PATH_MAX' undeclared (first use in this function)
     5567 |         char path[PATH_MAX];
          |                   ^~~~~~~~

    turbostat.c: In function 'probe_graphics':
    turbostat.c:6787:19: error: 'PATH_MAX' undeclared (first use in this function)
     6787 |         char path[PATH_MAX];
          |                   ^~~~~~~~

Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Reviewed-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>