This patch adds 3 wire transfer support to SPI mode list along with
its implementation.

3 wire or Bi-directional mode uses only one serial data pin for the
transfer. SPI in master mode uses MOSI data line only and MISO data
line is not used.
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>