bpf: Extract internal structs validation logic into helpers

bpf: Extract internal structs validation logic into helpers

The arraymap and hashtab duplicate the logic that checks for and frees
internal structs (timer, workqueue, task_work) based on
BTF record flags. Centralize this by introducing two helpers:

  * bpf_map_has_internal_structs(map)
    Returns true if the map value contains any of internal structs:
    BPF_TIMER | BPF_WORKQUEUE | BPF_TASK_WORK.

  * bpf_map_free_internal_structs(map, obj)
    Frees the internal structs for a single value object.

Convert arraymap and both the prealloc/malloc hashtab paths to use the
new generic functions. This keeps the functionality for when/how to free
these special fields in one place and makes it easier to add support for
new internal structs in the future without touching every map
implementation.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20251010164606.147298-3-mykyta.yatsenko5@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>