dts: quark_se_c1000_ss: Refactor dts.fixup into arch/arc/soc

Move common SoC dts.fixup defines into
arch/arc/soc/quark_se_c1000_ss/dts.fixup so we remove duplication in the
boards and only have board specific defines in
boards/arc/<FOO>/dts.fixup.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>