PCI: exynos: Remove deprecated PHY initialization code

Exynos platforms have a PCI PHY driver in the PHY framework that can be
used by the PCI host bridge drivers to initialize and manage the PHY.

Remove the deprecated PHY initialization code in the Exynos PCI host
bridge driver by updating the driver to use the PHY framework API;
modify the DT binding documentation accordingly.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>