arm: Make arch specific memcpy thumb-safe.

The current arch implementation of memcpy cannot be called
from thumb code, because it does not use bx instructions on return.
This patch addresses that. Note, that this patch does not touch
the hot loop of memcpy, so performance is not affected.

Tested on MXS (arm926ejs) with and without thumb-mode enabled.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>

arch/arm/lib/memcpy.S

@@ -59,7 +59,7 @@
 #endif
 ENTRY(memcpy)
 		cmp	r0, r1
-		moveq	pc, lr
+		bxeq	lr
 
 		enter	r4, lr
 
@@ -147,7 +147,8 @@ ENTRY(memcpy)
 		str1b	r0, r4, cs, abort=21f
 		str1b	r0, ip, cs, abort=21f
 
-		exit	r4, pc
+		exit	r4, lr
+		bx	lr
 
 9:		rsb	ip, ip, #4
 		cmp	ip, #2
@@ -256,7 +257,8 @@ ENTRY(memcpy)
 	.endm
 
 	.macro	copy_abort_end
-	ldmfd	sp!, {r4, pc}
+	ldmfd	sp!, {r4, lr}
+	bx	lr
 	.endm
 
 ENDPROC(memcpy)