arm: mxs: Correct CONFIG_SPL_NO_CPU_SUPPORT option

At present this is defined in Kconfig but there is a separate one in the
CONFIG whitelist. It looks like these are duplicates.

Rename the non-Kconfig one and remove it from the whitelist.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/arm/cpu/arm926ejs/Makefile b/arch/arm/cpu/arm926ejs/Makefile
index fdb0c92..b051025 100644
--- a/arch/arm/cpu/arm926ejs/Makefile
+++ b/arch/arm/cpu/arm926ejs/Makefile
@@ -7,7 +7,7 @@
 obj-y	= cpu.o cache.o
 
 ifdef	CONFIG_SPL_BUILD
-ifdef	CONFIG_SPL_NO_CPU_SUPPORT_CODE
+ifdef	CONFIG_SPL_NO_CPU_SUPPORT
 extra-y	:=
 endif
 endif