tty: serial: samsung: Remove USI initialization

USI control is now extracted to the dedicated USI driver. Remove USI
related code from serial driver to avoid conflicts and code duplication.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211204195757.8600-4-semen.protsenko@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>