configs: ls1028aqds: Move CONFIG_SPI_FLASH_* definitions to defconfig

LS1028A-QDS has CONFIG_SPI_FLASH_SST and CONFIG_SPI_FLASH_EON defines
present in header. Move these entries from header to defconfigs.

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>