timekeeping: Convert jiffies_seq to seqcount_raw_spinlock_t

Use the new api and associate the seqcounter to the jiffies_lock enabling
lockdep support - although for this particular case the write-side locking
and non-preemptibility are quite obvious.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201021190749.19363-1-dave@stgolabs.net