ARM: dts: exynos: add fake USB DWC3 supplies to SMDK5410

Add dummy/fake voltage regulators for USB DWC3 block on Exynos5410
SMDK5410 board.  These regulators are required by dtschema, however the
SMDK5410 board does not define the PMIC providing regulators.  Use dummy
fixed-regulators just to satisfy the dtschema checks.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220123111644.25540-11-krzysztof.kozlowski@canonical.com