mtd: rawnand: loongson: Add 6-byte NAND ID reading support

mtd: rawnand: loongson: Add 6-byte NAND ID reading support

Loongson-1C and Loongson-2K SoCs support NAND flash chips with 6-byte ID.
However, the current implementation only handles 5-byte ID which can lead
to incorrect chip detection.

Extend loongson_nand_read_id_type_exec() to support 6-byte NAND ID.

Signed-off-by: Keguang Zhang <keguang.zhang@gmail.com>
Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>