dt-bindings: phy: exynos: add the samsung,exynos-pcie-phy binding

dt-bindings: phy: exynos: add the samsung,exynos-pcie-phy binding

Add dt-bindings for the Samsung Exynos PCIe PHY controller (Exynos5433
variant). Based on the text dt-binding posted by Jaehoon Chung.

Link: https://lore.kernel.org/r/20201113170139.29956-4-m.szyprowski@samsung.com
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>