bpf: Include verifier memory allocations in memcg statistics

This commit adds __GFP_ACCOUNT flag to verifier induced memory
allocations. The intent is to account for all allocations reachable
from BPF_PROG_LOAD command, which is needed to track verifier memory
consumption in veristat. This includes allocations done in verifier.c,
and some allocations in btf.c, functions in log.c do not allocate.

There is also a utility function bpf_memcg_flags() which selectively
adds GFP_ACCOUNT flag depending on the `cgroup.memory=nobpf` option.
As far as I understand [1], the idea is to remove bpf_prog instances
and maps from memcg accounting as these objects do not strictly belong
to cgroup, hence it should not apply here.

(btf_parse_fields() is reachable from both program load and map
 creation, but allocated record is not persistent as is freed as soon
 as map_check_btf() exits).

[1] https://lore.kernel.org/all/20230210154734.4416-1-laoar.shao@gmail.com/



Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250613072147.3938139-2-eddyz87@gmail.com