mtd: rawnand: sunxi: merge register definitions for sunxi_nand{, _spl}.c

mtd: rawnand: sunxi: merge register definitions for sunxi_nand{, _spl}.c

Merge common register definitions from sunxi_nand{,_spl}.c

The Allwinner NAND controller registers where in both files, so let's
just merge all that in a header, it will be easier for maintenance.

NB: the defines are also harmonized with Linux driver

No functional change

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>