timerqueue: Provide linked timerqueue

timerqueue: Provide linked timerqueue

The hrtimer subsystem wants to peak ahead to the next and previous timer to
evaluated whether a to be rearmed timer can stay at the same position in
the RB tree with the new expiry time.

The linked RB tree provides the infrastructure for this as it maintains
links to the previous and next nodes for each entry in the tree.

Provide timerqueue wrappers around that.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163431.734827095@kernel.org