[MTD] orion_nand: add chip_delay parameter

Some SoCs need a different chip_delay value.

Signed-off-by: Saeed Bishara <saeed@marvell.com>
Acked-by: Jörn Engel <joern@logfs.org>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>