arm64: dts: exynos: TM2 - remove unused UART3 and set clocks directly on CMU

UART3 device is not really needed for enabling audio block on TM2.
Enabling it made it working by enabling some common parent clocks,
what is now handled by improved exynos5433 clocks driver. Thus the UART3
device node can be safely disabled. The assigned-clocks entries are
however still needed, so move them under the respective CMU node.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>