Merge branch 'bpf-reject-bpf_timer-for-preempt_rt'

Leon Hwang says:

====================
bpf: Reject bpf_timer for PREEMPT_RT

While running './test_progs -t timer' to validate the test case from
"selftests/bpf: Introduce experimental bpf_in_interrupt()"[0] for
PREEMPT_RT, I encountered a kernel warning:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48

To address this, reject bpf_timer usage in the verifier when
PREEMPT_RT is enabled, and skip the corresponding timer selftests.

Changes:
v2 -> v3:
* Drop skipping test case 'timer_interrupt'.
* Address comments from Alexei:
  * Respin targeting bpf tree.
  * Trim commit log.

v1 -> v2:
* Skip test case 'timer_interrupt'.

Links:
[0] https://lore.kernel.org/bpf/20250903140438.59517-1-leon.hwang@linux.dev/
====================

Link: https://patch.msgid.link/20250910125740.52172-1-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>