arm64: dts: marvell: turris-mox: drop unneeded flash address/size-cells

arm64: dts: marvell: turris-mox: drop unneeded flash address/size-cells

Flash node uses single "partition" node to describe partitions, so
remove deprecated address/size-cells properties to also fix dtc W=1
warnings:

  armada-3720-turris-mox.dts:218.10-255.4: Warning (avoid_unnecessary_addr_size): /soc/internal-regs@d0000000/spi@10600/flash@0: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>