phy: phy-mtk-tphy: make shared banks optional for V1 TPHY

V1 TPHY for SATA doesn't have shared banks if it isn't shared
with PCIe or USB, so make it optional.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>