select: add a poll specific struct to the restart_block union

with hrtimer poll/select, the signal restart data no longer is a single
long representing a jiffies count, but it becomes a second/nanosecond pair
that also needs to encode if there was a timeout at all or not.

This patch adds a struct to the restart_block union for this purpose

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>