dt-bindings: ata: atmel: remove at91 compact flash documentation

The compatible "at91rm9200-cf" is not used by any driver, hence remove the
corresponding documentation.

Signed-off-by: Hari Prasath Gujulan Elango <Hari.PrasathGE@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
[cassel: add missing space in commit log]
Signed-off-by: Niklas Cassel <cassel@kernel.org>