dt-bindings: serial: samsung: Make samsung,uart-fifosize a required property

Specifying samsung,uart-fifosize in both DT and driver static data is error
prone and relies on driver probe order and dt aliases to be correct.

Additionally on many Exynos platforms these are (USI) universal serial
interfaces which can be uart, spi or i2c, so it can change per board.

For google,gs101-uart make samsung,uart-fifosize a required property.
For this platform fifosize now *only* comes from DT.

Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Link: https://lore.kernel.org/r/20231211162331.435900-5-peter.griffin@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>