support DUAL and QUAD[patch v1]

[Gupta, Pekon]

> 
> Hi, Gupta
> 
> 
> > [Pekon]: Instead of adding new fields you can use existing 'mode' field to
> > pass on the platform specific configurations. And if 'u8 mode' does not
> > suffice you can increase it to 'u32'.
> > #define QSPI_MODE       1 << 5; // just check which bit-fields are un-used
> > spi_board_info->mode |= QSPI_MODE;
> >
> 
> well, can dual and quad be regarded as a spi mode? if so, your comment
> seems
> to be right.

Yes, Quad and Dual modes should be regarded as extension of SPI protocol.
- They follow the same basic principle of synchronous data transfer. Right ?
- These modes are not adding any extra side-band | In-band signaling or 
controls to modify the protocol. They are just increasing the width of
 data-channel for better throughput.

with regards, pekon