ARM: dts: imx: update sdma node name format

Node names should be generic, so change the sdma node name format 'sdma'
into 'dma-controller'.

Acked-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Joy Zou <joy.zou@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>