This is needed for an mmtimer driver update that we are currently working
on.  The mmtimer driver provides CLOCK_SGI_CYCLE via clock_gettime and
clock_settime.

With this api fix one will be able to use timer_create, timer_settime and
friends from userspace to schedule and receive signals via timer interrupts
of mmtimer.

Changelog
	* Clean up timer api for drivers that use register_posix_clock. Drivers
	  will then be able to use posix timers to schedule interrupts.
	* Change API for posix_clocks[].timer_create to only pass one pointer
	  to a k_itimer structure that is now allocated and managed by the
	  posix layer in the same way as for the other posix timer
	  functions.
	* Isolate a posix_timer_event(timr) function in posix-timers.c that may
	  be called by the interrupt routine of a timer to signal that the
	  scheduled event has taken place.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>