ARM: dts: r8a7792: move timer node out of bus

The timer node does not have any register properties and thus shouldn't be
placed on the bus.

This problem is flagged by the compiler as follows:
$ make dtbs W=1
...
  DTC     arch/arm/boot/dts/r8a7792-wheat.dtb
arch/arm/boot/dts/r8a7792-blanche.dtb: Warning (simple_bus_reg): Node /soc/timer missing or empty reg/ranges property
arch/arm/boot/dts/r8a7792-wheat.dtb: Warning (simple_bus_reg): Node /soc/timer missing or empty reg/ranges property

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>