used for MISO. Defaults to 1 if not present.
Some SPI controllers and devices support Dual and Quad SPI transfer mode.
-It allows data in SPI system transfered in 2 wires(DUAL) or 4 wires(QUAD).
+It allows data in the SPI system to be transferred in 2 wires(DUAL) or 4 wires(QUAD).
Now the value that spi-tx-bus-width and spi-rx-bus-width can receive is
only 1(SINGLE), 2(DUAL) and 4(QUAD).
Dual/Quad mode is not allowed when 3-wire mode is used.