dt-bindings: serial: samsung: Add ARTPEC-8 UART

Add a compatible for the UART on the ARTPEC-8 SoC. This hardware block
is closely related to the variants used on the Exynos chips. The
register layout is identical to Exynos850 et al but the fifo size is
different (64 bytes in each direction for all instances).

Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Vincent Whitchurch <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/samsung_uart.yaml

···
     items:
       - enum:
           - apple,s5l-uart
+          - axis,artpec8-uart
           - samsung,s3c2410-uart
           - samsung,s3c2412-uart
           - samsung,s3c2440-uart
···
           contains:
             enum:
               - apple,s5l-uart
+              - axis,artpec8-uart
               - samsung,exynos4210-uart
               - samsung,exynos5433-uart
     then: