dts: xtensa: nxp_imx8: add edma power domains

Add power domains for EDMA0's channels 6, 7, 14, and 15.
For QM these are identified as IMX_SC_R_DMA_2_*, while
for QXP thy are identified as IMX_SC_R_DMA_0_*.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>