drm: renesas: rz-du: mipi_dsi: Convert to RUNTIME_PM_OPS()

drm: renesas: rz-du: mipi_dsi: Convert to RUNTIME_PM_OPS()

Convert the Renesas RZ/G2L MIPI DSI Encoder driver from
SET_RUNTIME_PM_OPS() to RUNTIME_PM_OPS() and pm_ptr().  This lets us
drop the __maybe_unused annotations from its runtime suspend and resume
callbacks, and reduces kernel size in case CONFIG_PM is disabled.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/cdfc1b8ec9e62553654639b9e9026bfed8dd07d1.1752086582.git.geert+renesas@glider.be