make Linux bootable on ARM again

Commit 200b812d "Clear the exclusive monitor when returning from an
exception" broke the vast majority of ARM systems in the wild which are
still pre ARMv6.  The kernel is crashing on the first occurrence of an
exception due to the removal of the actual return instruction for them.
Let's add it back.
Signed-off-by: NNicolas Pitre <nico@marvell.com>
Acked-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/arm/kernel/entry-header.S

@@ -83,6 +83,8 @@
 	ldr	r0, [sp]
 	strex	r1, r2, [sp]			@ clear the exclusive monitor
 	ldmib	sp, {r1 - pc}^			@ load r1 - pc, cpsr
+#else
+	ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
 #endif
 	.endm