dt-bindings: display: ti,am65x-dss: Add am625 dss compatible

The DSS controller on TI's AM625 SoC is an update from that on TI's
AM65X SoC. The former has an additional OLDI TX on its first video port
that helps output cloned video or WUXGA (1920x1200@60fps) resolution
video output over a dual-link mode to reduce the required OLDI clock
output.

The second video port is same from AM65x DSS and it outputs DPI video
data. It can support 2K resolutions @ 60fps, independently.

Add the new controller's compatible and update descriptions.

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230616150900.6617-2-a-bhatia1@ti.com