perf: Use sample_flags for weight

Use the new sample_flags to indicate whether the weight field is filled
by the PMU driver.

Remove the weight field from the perf_sample_data_init() to minimize the
number of cache lines touched.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220901130959.1285717-5-kan.liang@linux.intel.com