"simple-panel" is a Linux driver and has never been an accepted upstream
compatible string, so remove it.

Cc: Heiko Stuebner <heiko@sntech.de>
Cc: linux-rockchip@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200117230851.25434-1-robh@kernel.orgSigned-off-by: Heiko Stuebner <heiko@sntech.de>