spl: nand: sunxi: split 'load page' and 'read page' logic

spl: nand: sunxi: split 'load page' and 'read page' logic

Split the 'load page' and 'read page' logic in 2 different functions so
we can later load the page and test different ECC configs without the
penalty of reloading the same page in the NAND cache.

We also move common setup to a dedicated function (nand_apply_config()) to
avoid rewriting the same values in NFC registers each time we read a page.

These new functions are passed a pointer to an nfc_config struct to limit
the number of parameters.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>