Fix the follow sparse warnings by adding missing headers:

drivers/gpu/drm/mediatek/mtk_cec.c:251:24: sparse: warning: symbol 'mtk_cec_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_ccorr.c:221:24: sparse: warning: symbol 'mtk_disp_ccorr_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_rdma.c:390:24: sparse: warning: symbol 'mtk_disp_rdma_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_gamma.c:209:24: sparse: warning: symbol 'mtk_disp_gamma_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_ovl.c:565:24: sparse: warning: symbol 'mtk_disp_ovl_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_color.c:164:24: sparse: warning: symbol 'mtk_disp_color_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_disp_aal.c:161:24: sparse: warning: symbol 'mtk_disp_aal_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_dpi.c:1109:24: sparse: warning: symbol 'mtk_dpi_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_hdmi_ddc.c:340:24: sparse: warning: symbol 'mtk_hdmi_ddc_driver' was not declared. Should it be static?
drivers/gpu/drm/mediatek/mtk_dsi.c:1223:24: sparse: warning: symbol 'mtk_dsi_driver' was not declared. Should it be static?
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20230110091647.13265-1-miles.chen@mediatek.com/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>