spi: Add support for dual and quad mode

spi bus can support dual and quad wire data transfers for tx and
rx. So defining dual and quad modes for both tx and rx. Also add
support to parse bus width used for spi tx and rx transfers.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>