hrtimer: Implement SOFT/HARD clock base selection

All prerequisites to handle hrtimers for expiry in either hard or soft
interrupt context are in place.

Add the missing bit in hrtimer_init() which associates the timer to the
hard or the softirq clock base.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: keescook@chromium.org
Link: http://lkml.kernel.org/r/20171221104205.7269-30-anna-maria@linutronix.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>