phy: mediatek: add helpers to update bits of registers

Add three helpers mtk_phy_clear/set/update_bits() for registers operation

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20211218082802.5256-3-chunfeng.yun@mediatek.com


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