perf symbols: Handle different endians properly during symbol load

perf symbols: Handle different endians properly during symbol load

Currently we dont care about the file object's endianness. It's possible
we read buildid file object from different architecture than we are
currentlly running on. So we need to care about properly reading such
object's data - handle different endianness properly.

Adding:
	needs_swap DSO field
	dso__swap_init function to initialize DSO's needs_swap
	DSO__SWAP to read the data with proper swaps

Together with other endianity patches, this change fixies perf report
discrepancies on origin and target systems as described in test 1 below,
e.g. following perf report diff:

...
      0.12%               ps  [kernel.kallsyms]    [k] clear_page
-     0.12%              awk  bash                 [.] alloc_word_desc
+     0.12%              awk  bash                 [.] yyparse
      0.11%   beah-rhts-task  libpython2.6.so.1.0  [.] 0x5560e
      0.10%             perf  libc-2.12.so         [.] __ctype_toupper_loc
-     0.09%  rhts-test-runne  bash                 [.] maybe_make_export_env
+     0.09%  rhts-test-runne  bash                 [.] 0x385a0
      0.09%               ps  [kernel.kallsyms]    [k] page_fault
...

Note, running following to test perf endianity handling:
test 1)
  - origin system:
    # perf record -a -- sleep 10 (any perf record will do)
    # perf report > report.origin
    # perf archive perf.data

  - copy the perf.data, report.origin and perf.data.tar.bz2
    to a target system and run:
    # tar xjvf perf.data.tar.bz2 -C ~/.debug
    # perf report > report.target
    # diff -u report.origin report.target

  - the diff should produce no output
    (besides some white space stuff and possibly different
     date/TZ output)

test 1)
  - origin system:
    # perf record -ag -fo /tmp/perf.data -- sleep 1
  - mount origin system root to the target system on /mnt/origin
  - target system:
    # perf script --symfs /mnt/origin -I -i /mnt/origin/tmp/perf.data \
     --kallsyms /mnt/origin/proc/kallsyms
  - complete perf.data header is displayed

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338380624-7443-2-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>