drm/mediatek: mtk_hdmi: Move N/CTS setting to new function

drm/mediatek: mtk_hdmi: Move N/CTS setting to new function

In preparation for splitting common bits of this driver, moving
the hdmi_rec_n_table struct array, and the hdmi_recommended_n(),
hdmi_mode_clock_to_hz(), hdmi_expected_cts() functions, add one
function called mtk_hdmi_get_ncts() that sets both N and CTS in
a single call.

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20250415104321.51149-12-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>