sunxi_nand_spl: Fix CONFIG_SPL_NAND_SUNXI handling

CONFIG_SPL_NAND_SUPPORT gets used via IS_ENABLED so it must be defined
to 1, rather then just being defined.

While at remove 2 other unused NAND related defines from sunxi-common.h.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>

include/configs/sunxi-common.h

@@ -138,15 +138,10 @@
 #define CONFIG_SERIAL_TAG
 
 #if defined(CONFIG_SPL_NAND_SUNXI)
-#define CONFIG_SPL_NAND_DRIVERS
-#define CONFIG_SPL_NAND_SUPPORT
-
-#define CONFIG_SYS_NAND_SPL_KERNEL_OFFS 0x280000
+#define CONFIG_SPL_NAND_SUPPORT 1
 #define CONFIG_SYS_NAND_U_BOOT_OFFS 0x008000
-
 #endif
 
-
 /* mmc config */
 #if !defined(CONFIG_UART0_PORT_F)
 #define CONFIG_MMC