support DUAL and QUAD[patch v1]

[yuhang wang]

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.