perf: Fix orphan callchain branches

Callchains have markers inside their capture to tell we
enter a context (kernel, user, ...).

Those are not displayed in the callchains but they are
incidentally an active part of the radix tree where
callchains are stored, just like any other address.

If we have the two following callchains:

addr1 -> addr2 -> user context -> addr3
addr1 -> addr2 -> user context -> addr4
addr1 -> addr2 -> addr 5

This is pretty common if addr1 and addr2 are part of an
interrupt path, addr3 and addr4 are user addresses and
addr5 is a kernel non interrupt path.

This will be stored as follows in the tree:

                   addr1
                   addr2
                   /   \
                  /     addr5
            user context
               /    \
             addr3  addr4

But we ignore the context markers in the report, hence
the addr3 and addr4 will appear as orphan branches:

    |--28.30%-- hrtimer_interrupt
    |          smp_apic_timer_interrupt
    |          apic_timer_interrupt
    |          |           <------------- here, no parent!
    |          |          |
    |          |          |--11.11%-- 0x7fae7bccb875
    |          |          |
    |          |          |--11.11%-- 0xffffffffff60013b
    |          |          |
    |          |          |--11.11%-- __pthread_mutex_lock_internal
    |          |          |
    |          |          |--11.11%-- __errno_location

Fix this by removing the context markers when we process the
callchains to the tree.

Reported-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1269274173-20328-1-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>