usb: dwc3: exynos: Add support for Exynos850 variant

Add Exynos850 compatible string and associated driver data. Only two
clocks are needed for this SoC:
  - bus_early: bus clock needed for registers access
  - ref: USB 2.0 DRD reference clock (50 MHz)

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230819031731.22618-4-semen.protsenko@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>