bpf: Convert hashtab.c to rqspinlock

bpf: Convert hashtab.c to rqspinlock

Convert hashtab.c from raw_spinlock to rqspinlock, and drop the hashed
per-cpu counter crud from the code base which is no longer necessary.

Closes: https://lore.kernel.org/bpf/675302fd.050a0220.2477f.0004.GAE@google.com
Closes: https://lore.kernel.org/bpf/000000000000b3e63e061eed3f6b@google.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-20-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>