phy: mediatek: mipi: remove register access helpers

Remove private register access helpers, use the common ones instead.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220920090038.15133-19-chunfeng.yun@mediatek.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>