dt-bindings: serial: snps-dw-apb-uart: add dma & dma-names properties

dt-bindings: serial: snps-dw-apb-uart: add dma & dma-names properties

Commit 0c559bc8abfb ("dt-bindings: serial: restrict possible child node
names") exposed the Allwinner D1 devicetrees as users of unevaluated
properties, with a slew of similar warnings now appearing during
dtbs_check:
sun20i-d1-nezha.dtb: serial@2500400: Unevaluated properties are not allowed ('dma-names', 'dmas' were unexpected)

Document the missing properties.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230208171715.70862-1-conor@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>