perf report: Add --symbols parameter

So that we can filter by symbol name.

The 'pfunct' utility in the 'dwarves' package can be used to
create a file with the functions one wants.

Example:

[acme@doppio pahole]$ pfunct /usr/lib/debug/usr/lib64/libdw-0.141.so.debug | grep dwarf > /tmp/dwarf.symbols
[acme@doppio pahole]$ wc -l /tmp/dwarf.symbols
93 /tmp/dwarf.symbols
[acme@doppio pahole]$ head -3 /tmp/dwarf.symbols
dwfl_addrdwarf
dwfl_module_getdwarf
dwfl_getdwarf
[acme@doppio pahole]$ perf report --sort comm,dso,symbol --comms pahole --dsos /usr/lib64/libdw-0.141.so --symbols file:///tmp/dwarf.symbols

    33.99%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_tag
    29.07%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_decl_file
    27.71%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_getsrclines
     4.54%            pahole  /usr/lib64/libdw-0.141.so  0x00000000007400
     3.93%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_decl_line
     0.46%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_getlocation
     0.18%            pahole  /usr/lib64/libdw-0.141.so  [.] __libdwarf_next_prime
     0.13%            pahole  /usr/lib64/libdw-0.141.so  [.] dwarf_diecu

[acme@doppio pahole]$

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1246399282-20934-4-git-send-email-acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>