bpf: enable stackmap with build_id in nmi context

bpf: enable stackmap with build_id in nmi context

Currently, we cannot parse build_id in nmi context because of
up_read(&current->mm->mmap_sem), this makes stackmap with build_id
less useful. This patch enables parsing build_id in nmi by putting
the up_read() call in irq_work. To avoid memory allocation in nmi
context, we use per cpu variable for the irq_work. As a result, only
one irq_work per cpu is allowed. If the irq_work is in-use, we
fallback to only report ips.

Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Signed-off-by: Song Liu <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>