tick/sched: Avoid hrtimer_cancel/start() sequence

The sequence of cancel and start is inefficient. It has to do the timer
lock/unlock twice and in the worst case has to reprogram the underlying
clock event device twice.

The reason why it is done this way is the usage of hrtimer_forward_now(),
which requires the timer to be inactive.

But that can be completely avoided as the forward can be done on a variable
and does not need any of the overrun accounting provided by
hrtimer_forward_now().

Implement a trivial forwarding mechanism and replace the cancel/reprogram
sequence with hrtimer_start(..., new_expiry).

For the non high resolution case the timer is not actually armed, but used
for storage so that code checking for expiry times can unconditially look
it up in the timer. So it is safe for that case to set the new expiry time
directly.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.542178086@kernel.org

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