drm: renesas: shmobile: Convert container helpers to static inline functions

Replace to conversion helper macros using container_of() by static
inline functions, to improve type-safety.

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/7d1f1aa4b832499f9e527353ce0ad6d84ff9a74a.1694767209.git.geert+renesas@glider.be