arm: mvebu: spl: Use preferred types u8/u16/u32 instead of uintN_t

Checkpatch warns about using uint32/16/8_t instead of u32/16/8.

Use the preferred types.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>