SPI: DUAL/QUAD support

[yuhang wang]

>                     if (!quad_mode)
>                             dra7xxx_writel(qspi, qspi->cmd | QSPI_RD_SNGL,
>                                             QSPI_SPI_CMD_REG);
>                     else
>                             dra7xxx_writel(qspi, qspi->cmd | QSPI_RD_QUAD,
>                                             QSPI_SPI_CMD_REG);
>                  .......
>                 }

So what do you based on to set variable quad_mode.