mtd: rawnand: qcom: embed nand_controller into qcom_nand_controller

mtd: rawnand: qcom: embed nand_controller into qcom_nand_controller

The qcom_nand_controller had a struct nand_controller *controller
pointer that was assigned to (struct nand_controller *)&nandc[1],
with the allocation oversized by sizeof(*controller) to make room.
get_qcom_nand_controller() then walked backwards from chip->controller
using sizeof()-based arithmetic to recover the enclosing nandc.

Embed the nand_controller directly into qcom_nand_controller and use
container_of() in get_qcom_nand_controller(). The header now needs
the full rawnand.h definition rather than a forward declaration.

Assisted-by: Claude:Opus-4.7
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>