There is no need to keep DMA controller nodes under AMBA bus node.
Remove the "amba" node to fix dtschema warnings like:

    amba: $nodename:0: 'amba' does not match '^(bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>