dt-bindings: serial: snps-dw-apb-uart: document RZ/N1 binding without DMA

dt-bindings: serial: snps-dw-apb-uart: document RZ/N1 binding without DMA

Renesas RZ/N1D has this UART with and without DMA support. Currently,
only the binding with DMA support is described. Add the missing one
without DMA support which can fallback even more.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250318085353.18990-2-wsa+renesas@sang-engineering.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>