perf/x86/vlbr: Add c->flags to vlbr event constraints

Just like what we do in the x86_get_event_constraints(), the
PERF_X86_EVENT_LBR_SELECT flag should also be propagated
to event->hw.flags so that the host lbr driver can save/restore
MSR_LBR_SELECT for the special vlbr event created by KVM or BPF.

Fixes: 097e4311

 ("perf/x86: Add constraint to create guest LBR event without hw counter")
Reported-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Like Xu <likexu@tencent.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Wanpeng Li <wanpengli@tencent.com>
Link: https://lore.kernel.org/r/20211103091716.59906-1-likexu@tencent.com