phy: ti-pipe3: use *syscon* framework API to set PCS value of the PHY

Deprecate using phy-omap-control driver to set PCS value of the PHY
and start using *syscon* API to do the same.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Acked-by: Rob Herring <robh@kernel.org>