intel_idle: shrink states tables

There is no reason to define CPUIDLE_STATE_MAX (currently 10) entries
in states tables if the driver always stops iterating over table when
it encounters first .enter == NULL entry.

$ size drivers/idle/intel_idle.o.*
   text    data     bss     dec     hex filename
   2886    5440      32    8358    20a6 drivers/idle/intel_idle.o.before
   2886    3752      32    6670    1a0e drivers/idle/intel_idle.o.after

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>