mtd: nand: davinci: fix driver registration

When kernel is booted using DT, there is no guarantee that Davinci
NAND device has been created already at the time when driver init
function is executed. Therefore, platform_driver_probe() can't be used
because this may result the Davinci NAND driver will never be probed.
The driver probing has to be made with core mechanism.

Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Taras Kondratiuk <taras@ti.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>