arm64: dts: renesas: r8a77970: move node which has no reg property out of bus

Move timer node from soc node to root node.  The node that have been moved
do not have any register properties and thus shouldn't be placed on the
bus.

This problem is flagged by the compiler as follows:
$ make W=1
...
  DTC     arch/arm64/boot/dts/renesas/r8a77970-eagle.dtb
arch/arm64/boot/dts/renesas/r8a77970-eagle.dtb: Warning (simple_bus_reg): Node /soc/timer missing or empty reg/ranges property
  DTC     arch/arm64/boot/dts/renesas/r8a77970-v3msk.dtb
arch/arm64/boot/dts/renesas/r8a77970-v3msk.dtb: Warning (simple_bus_reg): Node /soc/timer missing or empty reg/ranges property

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>