fs/timerfd: Use the new alarm/hrtimer functions

fs/timerfd: Use the new alarm/hrtimer functions

Like any other user controlled interface, timerfd based timers can be
programmed with expiry times in the past or vary small intervals.

Both hrtimer and alarmtimer provide new interfaces which return the queued
state of the timer. If the timer was already expired, then let the callsite
handle the timerfd context update so that the full round trip through the
hrtimer interrupt is avoided.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20260408114952.469141112@kernel.org