Move opp-table node from soc node to root node.

opp-table node does not have any register properties and thus
shouldn't be placed inside the bus.

This fixes the following build warnings with W=1:

arch/arm64/boot/dts/freescale/imx8mq.dtsi:687.28-703.5: Warning (simple_bus_reg): /soc@0/opp-table: missing or empty reg/ranges property

Fixes: 64d26f8c ("arm64: dts: imx8mq: Add the opp table and cores opp properties")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>