mtd: rawnand: Add an indirection on onfi_fill_interface_config()

This helper actually fills the interface configuration with SDR data.
As part of the work to bring NV-DDR support, let's rename this helper
onfi_fill_sdr_interface_config() and add a generic indirection to it.

There are no functional changes here, but this will simplify a next
change which adds onfi_fill_nvddr_interface_config() support.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-11-miquel.raynal@bootlin.com