phy: samsung: Merge Kconfig for Exynos5420 and Exynos5250

Exynos5420 variant of USB2 PHY is handled by the same code as the
Exynos5250 one. Introducing a separate Kconfig symbol for it was an
over-engineering, which turned out to cause build break for certain
configurations:

ERROR: modpost: "exynos5420_usb2_phy_config" [drivers/phy/samsung/phy-exynos-usb2.ko] undefined!

Fix this by removing PHY_EXYNOS5420_USB2 symbol and using
PHY_EXYNOS5250_USB2 also for Exynos5420 SoCs.

Reported-by: Markus Reichl <m.reichl@fivetechno.de>
Fixes: 81b534f7 ("phy: samsung: Add support for the Exynos5420 variant of the USB2 PHY")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Link: https://lore.kernel.org/r/20201202064759.24300-1-m.szyprowski@samsung.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>