ARM: dts: r9a06g032: Drop "arm,cortex-a7-timer" from timer node

"make dtbs_check":

    arch/arm/boot/dts/r9a06g032-rzn1d400-db.dt.yaml: timer: compatible: 'oneOf' conditional failed, one must be fixed:
	    ['arm,cortex-a7-timer', 'arm,armv7-timer'] is too long
	    'arm,cortex-a7-timer' is not one of ['arm,cortex-a15-timer']
	    'arm,cortex-a7-timer' is not one of ['arm,armv7-timer']
	    'arm,cortex-a7-timer' is not one of ['arm,armv8-timer']
	    From schema: Documentation/devicetree/bindings/timer/arm,arch_timer.yaml

The Cortex-A7 timer should just declare compatibility with
"arm,armv7-timer".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/a8e0cf00a983b4c539cdb1cfad5cc6b10b423c5b.1649680220.git.geert+renesas@glider.be