PCI: exynos: Support the PHY generic framework

Switch the pci-exynos driver to generic PHY framework.  At the same time
backward compatibility is preserved: Warning will be printed for old DTB.

Refer to the binding file:
- Documentation/devicetree/bindings/pci/samsung,exynos5440-pcie.txt

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>