soc: mediatek: Cleanup ifdefs for IS_REACHABLE(CONFIG_MTK_CMDQ)

Now that the mtk-cmdq.h header contains inline functions for cases
in which the driver is not enabled (either module or built-in), we
can safely go on with cleaning up ifdefs for CMDQ handling.

This also shows in a clearer manner that writing through CMDQ HW is
optional and used only for performance purposes when/where wanted,
needed and/or required.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230222094253.23678-10-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>