drm/mediatek: mtk_hdmi: Move vendor/product strings to drm_bridge

drm/mediatek: mtk_hdmi: Move vendor/product strings to drm_bridge

Move the vendor and product strings to the appropriate entries
of struct drm_bridge and use that in mtk_hdmi_setup_spd_infoframe
instead of having the same as function parameters.

While at it, also beautify the strings, setting them to read
"MediaTek On-Chip HDMI".

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20250217154836.108895-25-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>