drm/bridge: analogix_dp: Attach the next bridge in analogix_dp_bridge_attach()

drm/bridge: analogix_dp: Attach the next bridge in analogix_dp_bridge_attach()

Uniformly, move the next bridge attachment to the Analogix side
rather than scattered on Rockchip and Exynos sides. It can also
help get rid of the callback &analogix_dp_plat_data.attach() and
make codes more concise.

Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Heiko Stuebner <heiko@sntech.de> # rk3588
Link: https://patch.msgid.link/20260413132551.1049307-7-damon.ding@rock-chips.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>