drm/tilcdc: replace late_initcall with module_init

Use module_init instead of late_initcall, as is the norm for modular
drivers.

module_init was used until 6e8de0bd6a51fdeebd5d975c4fcc426f730b339b
("drm/tilcdc: add encoder slave (v2)") changed it to a late_initcall,
but it does not explain why. Tests show it's working properly with
module_init.

Signed-off-by: Guido Martínez <guido@vanguardiasur.com.ar>
Tested-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>