ENGR00227245 mx6q: Remove 400M setpoint for bus freq

ENGR00227245 mx6q: Remove 400M setpoint for bus freq

Although 400M bus setpoint can save some SOC domain power,
but it will also bring some additional power consumption
to DDR3, and the DDR performace's drop could also lead to
more heat generated by COREs which will spent more time
waiting for DDR data ready, also, there is not many usecases
that need this setpoint, all in all, we should remove 400M
setpoint.

Signed-off-by: Anson Huang <b20788@freescale.com>