ARM: 8610/1: V7M: Add dsb before jumping in handler mode

According to ARM AN321 (section 4.12):

"If the vector table is in writable memory such as SRAM, either relocated
by VTOR or a device dependent memory remapping mechanism, then
architecturally a memory barrier instruction is required after the vector
table entry is updated, and if the exception is to be activated
immediately"

Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/proc-v7m.S

@@ -132,6 +132,7 @@ __v7m_setup_cont:
 	badr	r1, 1f
 	ldr	r5, [r12, #11 * 4]	@ read the SVC vector entry
 	str	r1, [r12, #11 * 4]	@ write the temporary SVC vector entry
+	dsb
 	mov	r6, lr			@ save LR
 	ldr	sp, =init_thread_union + THREAD_START_SP
 	cpsie	i