fix compilation of i.MX31 platforms

mxc_iomux_v3_init() is defined in arch/arm/plat-mxc/iomux-v3.c, which is
not linked for i.MX31 and produces an undefined reference error. Fix this
by building the offending code only for i.MX35.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/mach-mx3/mm.c

@@ -81,6 +81,7 @@ void __init mx31_map_io(void)
 	iotable_init(mxc_io_desc, ARRAY_SIZE(mxc_io_desc));
 }
 
+#ifdef CONFIG_ARCH_MX35
 void __init mx35_map_io(void)
 {
 	mxc_set_cpu_type(MXC_CPU_MX35);
@@ -89,6 +90,7 @@ void __init mx35_map_io(void)
 
 	iotable_init(mxc_io_desc, ARRAY_SIZE(mxc_io_desc));
 }
+#endif
 
 void __init mx31_init_irq(void)
 {