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/Makefile b/Makefile
index f405b25..0167a6c 100644
--- a/Makefile
+++ b/Makefile
@@ -653,7 +653,7 @@
 # Add GCC lib
 ifdef USE_PRIVATE_LIBGCC
 ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
-PLATFORM_LIBGCC = $(OBJTREE)/arch/$(ARCH)/lib/lib.a
+PLATFORM_LIBGCC = arch/$(ARCH)/lib/lib.a
 else
 PLATFORM_LIBGCC = -L $(USE_PRIVATE_LIBGCC) -lgcc
 endif