kbuild: use SoC-specific CONFIG to descend into SoC directory

Use "obj-$(CONFIG_FOO) += foo/" where it is possible.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
index d2488e7..0c10223 100644
--- a/arch/arm/cpu/armv8/Makefile
+++ b/arch/arm/cpu/armv8/Makefile
@@ -15,4 +15,4 @@
 obj-y	+= tlb.o
 obj-y	+= transition.o
 
-obj-y += $(if $(SOC),$(SOC)/)
+obj-$(CONFIG_FSL_LSCH3) += fsl-lsch3/