ARM: imx6q: move clock register map to machine_desc.map_io

map_io is the only place to call iotable_init.

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
[shawn.guo: rename imx_clock_map_io() to imx6q_clock_map_io()]
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>