ARM: dts: exynos: replace hardcoded reserved memory ranges with auto-allocated ones

Generic reserved memory regions bindings allow to automatically allocate
region of given parameters (alignment and size), so use this feature
instead of the hardcoded values, which had no dependency on the real
hardware. This patch also increases "left" region from 8MiB to 16MiB to
make the codec really usable with nowadays steams (with 8MiB reserved
region it was not even possible to decode 480p H264 video).

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>