ColdFire: Cleanup for partial linking and --gc-sections

Introduce the --gc-sections for ColdFire platform and clean up the
corresponding lds file.

Signed-off-by: TsiChung Liew <tsicliew@gmail.com>
Signed-off-by: Jason Jin <Jason.jin@freescale.com>
diff --git a/arch/m68k/config.mk b/arch/m68k/config.mk
index 863f3dd..81b14c2 100644
--- a/arch/m68k/config.mk
+++ b/arch/m68k/config.mk
@@ -28,3 +28,5 @@
 
 PLATFORM_CPPFLAGS += -DCONFIG_M68K -D__M68K__
 PLATFORM_LDFLAGS  += -n
+PLATFORM_RELFLAGS              += -ffunction-sections -fdata-sections
+LDFLAGS_FINAL                  += --gc-sections