Fix Makefile for ARMv8-A AArch32 build

Commit 26e63c44

 broke the Makefile for ARMv8-A AArch32 platforms.
This patch fixes it.

Change-Id: I49b8eb5b88f3a131aa4c8642ef970e92d90b6dd2
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

Makefile

@@ -131,7 +131,7 @@ target32-directive	= 	-target arm-none-eabi
 # Will set march32-directive from platform configuration
 else
 target32-directive	= 	-target armv8a-none-eabi
-march32-directive	= 	-march armv8-a
+march32-directive	= 	-march=armv8-a
 endif
 
 ifeq ($(notdir $(CC)),armclang)