ARM: dts: exynos: add USB DWC3 supplies to SMDK5420

Add required voltage regulators for USB DWC3 block on Exynos5420
SMDK5420 board.  Due to lack of board schematics, use same
regulators as on ArndaleOcta board.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220123111644.25540-10-krzysztof.kozlowski@canonical.com