kbuild: consolidate PLATFORM_LIBS

We had switched to Kbuild so now we can specify
PLATFORM_LIBS/PLATFORM_LIBGCC with relative path.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Tom Rini <trini@ti.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/spl/Makefile b/spl/Makefile
index 346d0aa..57bd43b 100644
--- a/spl/Makefile
+++ b/spl/Makefile
@@ -133,7 +133,7 @@
 
 # Add GCC lib
 ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
-PLATFORM_LIBGCC = $(SPLTREE)/arch/$(ARCH)/lib/lib.a
+PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a
 PLATFORM_LIBS := $(filter-out %/lib.a, $(filter-out -lgcc, $(PLATFORM_LIBS))) $(PLATFORM_LIBGCC)
 endif