mtd: rawnand: sunxi_spl: Fix cast to pointer from integer warnings

mtd: rawnand: sunxi_spl: Fix cast to pointer from integer warnings

Fix a cast to pointer from integer warning on ARM64

On 64bits platform, the casts done in {read,write}l() give that kind of
warnings:
drivers/mtd/nand/raw/sunxi_nand_spl.c: In function ‘check_value_inner’:
./arch/arm/include/asm/io.h:110:43: warning: cast to pointer from \
integer of different size [-Wint-to-pointer-cast]
  110 | #define __raw_readl(a) (*(volatile unsigned int *)(a))
      |                          ^
[...]
drivers/mtd/nand/raw/sunxi_nand_spl.c:81:27: note: in expansion of \
macro ‘readl’
   81 |                 int val = readl(offset) & expected_bits;

Introduce {read,write}l_nfc inline function to do the right cast and
push the base address (SUNXI_NFC_BASE) into those functions, making the
code more readable.

Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>