dt-bindings: phy: mediatek: tphy: add support hardware version 3

The PHYA architecture is updated, and doesn't support slew rate
calibration anymore on 7nm or advanced process, add a new version
number to support it.
Due to the FreqMeter bank is not used but reserved, it's backward
with v2 until now.
For mt8195, no function changes when use generic v2 or v3 compatible,
but prefer to use v3's compatible, it will not waste the time to
calibrate the slew rate, and also correspond with hardware version.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1627028562-23584-1-git-send-email-chunfeng.yun@mediatek.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>