drm/stm: dsi: move lane capability detection in probe()

There is no need to re-compute the dsi lane capability because it
only depends on dsi hw version.
Since dsi hw version is detected at probe(), move there also the
assignment of dsi lane capability.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Acked-by: Philippe Cornu <philippe.cornu@foss.st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@foss.st.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211218215055.212421-1-antonio.borneo@foss.st.com