phy: mediatek: tphy: remove macros to prepare bitfield value

Prefer to make use of FIELD_PREP() macro to prepare bitfield value,
then no need local ones anymore.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20220920090038.15133-3-chunfeng.yun@mediatek.comSigned-off-by: Vinod Koul <vkoul@kernel.org>