phy: phy-exynos-pcie: Add support for Exynos PCIe PHY

Add support for Generic PHY framework about Exynos SoCs.  Current Exynos
PCIe driver doesn't use the PHY framework, which makes it difficult to
upstream the other Exynos variants because of different PHY registers.

Move the codes relevant to PHY from Exnyos PCIe driver to PHY Exynos PCIe
driver.

[bhelgaas: depend on "OF && (ARCH_EXYNOS || COMPILE_TEST)", update
copyright year, both per Vivek]
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>