ENGR00176068-1 mx6q: add smp_twd clock for localtimer

ENGR00176068-1 mx6q: add smp_twd clock for localtimer

Add a smp_twd system clock which is simple clock
from parent of cpu_clk, and it's rate is half
of the cpu_clk.
This is used for reprograming the twd clock event
after cpu freq is changed.
Also disable local timer setup when wait mode enabled.

Signed-off-by: Xinyu Chen <xinyu.chen@freescale.com>