soc: mediatek: cmdq: add write_s value function

add write_s function in cmdq helper functions which
writes a constant value to address with large dma
access support.

Signed-off-by: Dennis YC Hsieh <dennis-yc.hsieh@mediatek.com>
Link: https://lore.kernel.org/r/1594136714-11650-6-git-send-email-dennis-yc.hsieh@mediatek.com


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