mtd: nand: raw: rockchip_nfc: fix oobfree offset and description

mtd: nand: raw: rockchip_nfc: fix oobfree offset and description

The MTD framework reserves 1 or 2 bytes for the bad block marker
depending on the bus size. The rockchip_nfc driver currently only
supports a 8 bit bus, but reserves standard 2 bytes for the BBM.
The first free OOB byte is therefore OOB2 at offset 2.
Page address(PA) bytes are moved to the last 4 positions before
ECC. Update the description for U-boot.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>