imx: Drop unused CONFIG_IMX

This option does not exist, so the Makefile rule does nothing. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/arm920t/Makefile b/arch/arm/cpu/arm920t/Makefile
index b70822c..5ac3740 100644
--- a/arch/arm/cpu/arm920t/Makefile
+++ b/arch/arm/cpu/arm920t/Makefile
@@ -7,8 +7,6 @@
 
 obj-y	+= cpu.o
 
-obj-$(CONFIG_IMX) += imx/
-
 # some files can only build in ARM mode
 
 ifdef CONFIG_$(SPL_)SYS_THUMB_BUILD