drivers/timer: New ARM SysTick driver

Newer, and much smaller driver written to the new timer API.  Supports
all the features the old one did (including shutting off the clock
when clock_always_on is disabled), should be faster in practice, and
should be significantly more accurate due to the "lost cycle" trick
applied in z_clock_set_timeout().

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>