perf: Consolidate branch sample filter helpers

Besides the branch type filtering requests, 'event.attr.branch_sample_type'
also contains various flags indicating which additional information should
be captured, along with the base branch record. These flags help configure
the underlying hardware, and capture the branch records appropriately when
required e.g after PMU interrupt. But first, this moves an existing helper
perf_sample_save_hw_index() into the header before adding some more helpers
for other branch sample filter flags.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220906084414.396220-1-anshuman.khandual@arm.com