perf symbols: Refactor vmlinux_path__init() to ease path additions

perf symbols: Refactor vmlinux_path__init() to ease path additions

Refactor vmlinux_path__init() to ease subsequent additions of new
vmlinux locations.

Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
Acked-by: Alexander Yarygin <yarygin@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1448469166-61363-2-git-send-email-tumanova@linux.vnet.ibm.com
[ Rename vmlinux_path__update() to vmlinux_path__add() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>