Convert CONFIG_NAND_MXS to Kconfig

configs/apx4devkit_defconfig

configs/aristainetos2_defconfig

configs/aristainetos2b_defconfig

configs/aristainetos_defconfig

configs/bg0900_defconfig

configs/cm_fx6_defconfig

configs/colibri_imx7_defconfig

configs/gwventana_nand_defconfig

configs/m28evk_defconfig

configs/mx28evk_auart_console_defconfig

configs/mx28evk_defconfig

configs/mx28evk_nand_defconfig

configs/mx28evk_spi_defconfig

configs/mx6sabreauto_defconfig

configs/mx6sxsabreauto_defconfig

configs/pcm058_defconfig

configs/pfla02_defconfig

configs/platinum_picon_defconfig

configs/platinum_titanium_defconfig

configs/titanium_defconfig