soc: mediatek: cmdq: Add inline functions for !CONFIG_MTK_CMDQ

In preparation for a cleanup of ifdef instances of IS_REACHABLE() for
the CONFIG_MTK_CMDQ configuration option, add inline functions that
will either return a failure or, for void functions, do nothing.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230222094253.23678-9-angelogioacchino.delregno@collabora.com


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