ARM: mxs: get reset address from device tree

Instead of using static address definition, get reset address from
device tree with mapping, so that core_initcall mxs_arch_reset_init()
can be killed.

The "rtc" clock code in mxs_arch_reset_init() seems to be zombie, since
there is no clk lookup defined in clock driver at all.  Remove it
together.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>