ARM: mxs: Remove unused variable warning

Shuffle the macros around a little to remove the following warning
when building for i.MX28:

arch/arm/cpu/arm926ejs/mxs/spl_boot.c:44:26: warning: ‘iomux_boot’ defined but not used [-Wunused-const-variable=]
 static const iomux_cfg_t iomux_boot[] = {
                          ^~~~~~~~~~

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Stefano Babic <sbabic@denx.de>

arch/arm/cpu/arm926ejs/mxs/spl_boot.c

@@ -40,17 +40,17 @@ void early_delay(int delay)
 		;
 }
 
+#if defined(CONFIG_MX23)
 #define	MUX_CONFIG_BOOTMODE_PAD	(MXS_PAD_3V3 | MXS_PAD_4MA | MXS_PAD_NOPULL)
 static const iomux_cfg_t iomux_boot[] = {
-#if defined(CONFIG_MX23)
 	MX23_PAD_LCD_D00__GPIO_1_0 | MUX_CONFIG_BOOTMODE_PAD,
 	MX23_PAD_LCD_D01__GPIO_1_1 | MUX_CONFIG_BOOTMODE_PAD,
 	MX23_PAD_LCD_D02__GPIO_1_2 | MUX_CONFIG_BOOTMODE_PAD,
 	MX23_PAD_LCD_D03__GPIO_1_3 | MUX_CONFIG_BOOTMODE_PAD,
 	MX23_PAD_LCD_D04__GPIO_1_4 | MUX_CONFIG_BOOTMODE_PAD,
 	MX23_PAD_LCD_D05__GPIO_1_5 | MUX_CONFIG_BOOTMODE_PAD,
-#endif
 };
+#endif
 
 static uint8_t mxs_get_bootmode_index(void)
 {