drm/omap/dss: Use of_property_present() to test existence of DT property

of_property_read_bool() should be used only on boolean properties.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250114145840.505459-1-krzysztof.kozlowski@linaro.org