When looking at a callchains enabled perf data file one can find it
tiresome to start with all callchains collapsed and then to have to go
one by one expanding them.

So associate 'E' with "Expand all callchains" and 'C' with "Collapse all
callchains".

This way now one can have the top level view and then switch to/from
having all callchains expanded.

More work is needed to allow expanding just from one branch down to its
leaves.
Reported-by: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>