To support DM QSPI driver:
- Add -u-boot.dtsi to modify n25q256a@0 and n25q256a@1 compatible string
to "spi-flash" and add "num-cs" property.
- Enable DM SPI and DM SPI FLASH configurations
- Remove iomux settings of qspi1 in board codes which is not needed
for DM driver.
Signed-off-by: Ye Li <ye.li@nxp.com>