devicetree:bindings: add devicetree bindings for ceva ahci

adds bindings for CEVA AHCI SATA controller. optional property
broken-gen2 is useful incase of hardware speed limitation.

Signed-off-by: Suneel Garapati <suneel.garapati@xilinx.com>
Signed-off-by: Tejun Heo <tj@kernel.org>