clk: mxs: get base address from device tree

Instead of using the static definitions, get clkctrl and digctl base
addresses with mapping from device tree.

Use macro on variable is not nice, but it's done here to save huge
pointless diff stat.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Mike Turquette <mturquette@linaro.org>