[PATCH] SPI: DUAL and QUAD support

[Gupta, Pekon]

> 2. I don't think that  SPI_NBITS_SINGLE_HALF_DUPLEX is necessary.
> tx_nbits and rx_nbits in @spi_transfer should be passed to spi master
> driver and the master driver will set the certain mode depend on the
> info in @spi_transfer. So there is no need to let the master driver
> know SPI_NBITS_SINGLE_HALF_DUPLEX, also master can get the 3-wire SPI
> info from spi_device->mode.
I should have been more explicit here.. it would be good it you replace
'spi_device->mode & SPI_3_WIRE' with your above mode & tx_nbit, rx_nbits
so that the channel width information becomes consistent for all modes.
All mode bit flags in same octet look better.

with regards, pekon