mtd: rawnand: omap_gpmc: support u-boot driver model

mtd: rawnand: omap_gpmc: support u-boot driver model

Adds driver model support.

We need to be able to self initialize the NAND controller/chip
at probe and so enable CONFIG_SYS_NAND_SELF_INIT.

Doing so requires nand_register() API which is provided by nand.c
and needs to be enabled during SPL build via CONFIG_SPL_NAND_INIT.
But nand.c also provides nand_init() so we need to get rid of nand_init()
in omap_gpmc driver if CONFIG_SPL_NAND_INIT is set.

Signed-off-by: Roger Quadros <[email protected]>
Signed-off-by: Michael Trimarchi <[email protected]>
Signed-off-by: Dario Binacchi <[email protected]>
Link: https://lore.kernel.org/all/[email protected]