ath79: add back NAND symbols to NAND target

The NAND config symbols were removed unintentionally while adding
support for Linux 5.4.

Add the respective symbols for v4.19 as well as v5.4.

Signed-off-by: David Bauer <mail@david-bauer.net>

target/linux/ath79/nand/config-default

@@ -5,7 +5,10 @@ CONFIG_CRYPTO_HASH_INFO=y
 CONFIG_CRYPTO_LZO=y
 CONFIG_LZO_COMPRESS=y
 CONFIG_LZO_DECOMPRESS=y
+CONFIG_MTD_NAND=y
+CONFIG_MTD_NAND_AR934X=y
 CONFIG_MTD_NAND_CORE=y
+CONFIG_MTD_RAW_NAND=y
 CONFIG_MTD_SPI_NAND=y
 CONFIG_MTD_SPLIT_MINOR_FW=y
 CONFIG_MTD_UBI=y