dt-bindings: mfd: ti,am3359-tscadc: Allow dmas property to be optional

dt-bindings: mfd: ti,am3359-tscadc: Allow dmas property to be optional

ADC module can function without DMA, so there may not be dma channel
always associated with device. Hence, remove "dmas", "dma-names" from list
of required properties.

Signed-off-by: Santhosh Kumar K <s-k6@ti.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20231124045019.21003-1-s-k6@ti.com
Signed-off-by: Lee Jones <lee@kernel.org>