Use --gc-sections during link

All common functions are being built into all binary images,
whether or not they are actually used. This change enables the
use of -ffunction-sections, -fdata-sections and --gc-sections
in the compiler and linker to remove unused code and data from
the images.

Change-Id: Ia9f78c01054ac4fa15d145af38b88a0d6fb7d409
diff --git a/Makefile b/Makefile
index 9d02141..f4b74fe 100644
--- a/Makefile
+++ b/Makefile
@@ -150,8 +150,10 @@
 CFLAGS			:= 	-nostdinc -pedantic -ffreestanding -Wall	\
 				-Werror -mgeneral-regs-only -std=c99 -c -Os	\
 				-DDEBUG=${DEBUG} ${INCLUDES} ${CFLAGS}
+CFLAGS			+=	-ffunction-sections -fdata-sections
 
 LDFLAGS			+=	--fatal-warnings -O1
+LDFLAGS			+=	--gc-sections
 
 
 vpath %.ld.S bl1:bl2:bl31