imx6: don't include unneeded boot_mode array in SPL

The soc_boot_modes array is only used by bmode command
and not needed in SPL. Don't include it into SPL.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/mach-imx/mx6/soc.c b/arch/arm/mach-imx/mx6/soc.c
index f8bc05e..b724668 100644
--- a/arch/arm/mach-imx/mx6/soc.c
+++ b/arch/arm/mach-imx/mx6/soc.c
@@ -551,6 +551,7 @@
 }
 #endif
 
+#ifndef CONFIG_SPL_BUILD
 /*
  * cfg_val will be used for
  * Boot_cfg4[7:0]:Boot_cfg3[7:0]:Boot_cfg2[7:0]:Boot_cfg1[7:0]
@@ -577,6 +578,7 @@
 	{"esdhc4",	MAKE_CFGVAL(0x40, 0x38, 0x00, 0x00)},
 	{NULL,		0},
 };
+#endif
 
 void reset_misc(void)
 {