ARM: dts: exynos: add USB DWC3 supplies to Chromebook Spring

Add required voltage regulators for USB DWC3 block on Exynos5250
Chromebook Spring board.  Due to lack of board schematics, use same
regulators as on Arndale board.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220123111644.25540-6-krzysztof.kozlowski@canonical.com