arm: lib: memcpy: Do not copy to same address

In some cases (e.g. bootm with a elf payload which is already at the right
position) there is a in place copy of data to the same address. Catching this
saves some ms while booting.

Signed-off-by: Matthias Weisser <weisserm@arcor.de>

arch/arm/lib/memcpy.S

@@ -60,6 +60,9 @@
 .globl memcpy
 memcpy:
 
+		cmp	r0, r1
+		moveq	pc, lr
+
 		enter	r4, lr
 
 		subs	r2, r2, #4