dt-bindings: cadence-quadspi: Add new compatible for AM654 SoC

AM654 SoC has Cadence Octal SPI controller, which is similar to Cadence
QSPI controller but supports Octal IO(x8 data lines) and Double Data
Rate(DDR) mode. Add new compatible to support OSPI controller on TI's
AM654 SoCs.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>