mtd: rawnand: gpmi: Fix the driver only sense CS0 R/B issue

Set the GPMI CTRL1 GANGED_RDYBUSY bit so driver can sense the R/B signal
from all CS.

For the NAND chip MT29F64G08AFAAAWP, only the first chip detected
without the patch.

[    3.764118] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0x68
[    3.770613] nand: Micron MT29F64G08AFAAAWP
[    3.774752] nand: 4096 MiB, SLC, erase size: 1024 KiB, page size: 8192, OOB size: 448
[    3.786421] Bad block table found at page 524160, version 0x01
[    3.792730] Bad block table found at page 524032, version 0x01

After applying the patch

[    3.764445] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0x68
[    3.770941] nand: Micron MT29F64G08AFAAAWP
[    3.775080] nand: 4096 MiB, SLC, erase size: 1024 KiB, page size: 8192, OOB size: 448
[    3.784390] nand: 2 chips detected
[    3.790900] Bad block table found at page 524160, version 0x01
[    3.796776] Bad block table found at page 1048448, version 0x01

Signed-off-by: Han Xu <han.xu@nxp.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201209035104.22679-2-han.xu@nxp.com