drm/tilcdc: add missing header dependencies

We get 4 warnings when building kernel with W=1:
drivers/gpu/drm/tilcdc/tilcdc_tfp410.c:393:12: warning: no previous prototype for 'tilcdc_tfp410_init' [-Wmissing-prototypes]
drivers/gpu/drm/tilcdc/tilcdc_tfp410.c:398:13: warning: no previous prototype for 'tilcdc_tfp410_fini' [-Wmissing-prototypes]
drivers/gpu/drm/tilcdc/tilcdc_panel.c:443:12: warning: no previous prototype for 'tilcdc_panel_init' [-Wmissing-prototypes]
drivers/gpu/drm/tilcdc/tilcdc_panel.c:448:13: warning: no previous prototype for 'tilcdc_panel_fini' [-Wmissing-prototypes]

In fact, these functions are declared in
drivers/gpu/drm/tilcdc/tilcdc_tfp410.h,
drivers/gpu/drm/tilcdc/tilcdc_panel.h,
so this patch adds missing header dependencies.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Signed-off-by: Jyri Sarha <jsarha@ti.com>