ARM: 8670/1: V7M: Do not corrupt vector table around v7m_invalidate_l1 call

We save/restore registers around v7m_invalidate_l1 to address pointed
by r12, which is vector table, so the first eight entries are
overwritten with a garbage. We already have stack setup at that stage,
so use it to save/restore register.

Fixes: 6a8146f420 ("ARM: 8609/1: V7M: Add support for the Cortex-M7 processor")
Cc: <stable@vger.kernel.org>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/mm/proc-v7m.S

@@ -147,10 +147,10 @@ __v7m_setup_cont:
 
 	@ Configure caches (if implemented)
 	teq     r8, #0
-	stmneia	r12, {r0-r6, lr}	@ v7m_invalidate_l1 touches r0-r6
+	stmneia	sp, {r0-r6, lr}		@ v7m_invalidate_l1 touches r0-r6
 	blne	v7m_invalidate_l1
 	teq     r8, #0			@ re-evalutae condition
-	ldmneia	r12, {r0-r6, lr}
+	ldmneia	sp, {r0-r6, lr}
 
 	@ Configure the System Control Register to ensure 8-byte stack alignment
 	@ Note the STKALIGN bit is either RW or RAO.