drm/sun4i: hdmi: Move mode_set into enable

We're not doing anything special in atomic_mode_set so we can simply
merge it into atomic_enable.

Acked-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240222-kms-hdmi-connector-state-v7-33-8f4af575fce2@kernel.org