ARM: dts: at91: use generic node name for dataflash

The node names should be generic, so use "flash" for dataflash nodes and
for cfi-flash.

Suggested-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220412105013.249793-1-krzysztof.kozlowski@linaro.org