drm/mediatek: dsi: Add atomic {destroy,duplicate}_state, reset callbacks

Add callbacks for atomic_destroy_state, atomic_duplicate_state and
atomic_reset to restore functionality of the DSI driver: this solves
vblank timeouts when another bridge is present in the chain.

Tested bridge chain: DSI <=> ANX7625 => aux-bus panel

Fixes: 7f6335c6 ("drm/mediatek: Modify dsi funcs to atomic operations")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>