phy: mediatek: tphy: add debugfs files

These debugfs files are mainly used to make eye diagram test easier,
especially helpful to do HQA test for a new IC without efuse enabled.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/20230513092218.21139-2-chunfeng.yun@mediatek.com


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