riscv: k210: Enable QSPI for spi3

This device has four IOs connected to the SPI flash. Add the appropriate
bindings.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Leo Liang <ycliang@andestech.com>
diff --git a/arch/riscv/dts/k210-maix-bit.dts b/arch/riscv/dts/k210-maix-bit.dts
index e4dea20..902dcfd 100644
--- a/arch/riscv/dts/k210-maix-bit.dts
+++ b/arch/riscv/dts/k210-maix-bit.dts
@@ -200,6 +200,8 @@
 		compatible = "jedec,spi-nor";
 		reg = <0>;
 		spi-max-frequency = <50000000>;
+		spi-tx-bus-width = <4>;
+		spi-rx-bus-width = <4>;
 		m25p,fast-read;
 		broken-flash-reset;
 	};