perf ftrace latency: Add -e option to measure time between two events

perf ftrace latency: Add -e option to measure time between two events

In addition to the function latency, it can measure events latencies.
Some kernel tracepoints are paired and it's menningful to measure how
long it takes between the two events.  The latency is tracked for the
same thread.

Currently it only uses BPF to do the work but it can be lifted later.
Instead of having separate a BPF program for each tracepoint, it only
uses generic 'event_begin' and 'event_end' programs to attach to any
(raw) tracepoints.

  $ sudo perf ftrace latency -a -b --hide-empty \
    -e i915_request_wait_begin,i915_request_wait_end -- sleep 1
  #   DURATION     |      COUNT | GRAPH                                |
     256 -  512 us |          4 | ######                               |
       2 -    4 ms |          2 | ###                                  |
       4 -    8 ms |         12 | ###################                  |
       8 -   16 ms |         10 | ################                     |

  # statistics  (in usec)
    total time:               194915
      avg time:                 6961
      max time:                12855
      min time:                  373
         count:                   28

Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250714052143.342851-1-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>