hrtimer: Cleanup coding style and comments

As this code has some major surgery ahead, clean up coding style and bring
comments up to date.

No functional change intended.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163430.342740952@kernel.org