posix-timers: Add support for fd based clocks

Extend the negative clockids which are currently used by posix cpu
timers to encode the PID with a file descriptor based type which
encodes the fd in the upper bits.

Originally-from: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <johnstul@us.ibm.com>
LKML-Reference: <20110201134420.062860200@linutronix.de>

diff --cc include/linux/posix-timers.h
Simple merge

diff --cc kernel/posix-timers.c
Simple merge