configs: Move CONFIG_SPI_FLASH into defconfigs

Completely move CONFIG_SPI_FLASH from remaining board header files to
defconfigs

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> #zynq-microzed