The bootloader will fix up the IOMMU entries only on nodes with the
compatible "fsl,vf610-edma". Thus make this compatible string mandatory
for the ls1028a-edma.

While at it, fix the "fsl,fsl," typo.
Signed-off-by: Michael Walle <michael@walle.cc>
Fixes: d8c1bdb5 ("dt-bindings: dma: fsl-edma: add new fsl,fsl,ls1028a-edma")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>