arm64: dts: exynos: Rename Multi Core Timer node to "timer" on Exynos5433

The device node name should reflect generic class of a device so rename
the Multi Core Timer node from "mct" to "timer".  This will be also in
sync with upcoming DT schema.  No functional change.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>