armv7: psci: cpu_off: flush D-Cache before disable D-Cache

Before disable cache, need to first flush cache.

There maybe dirty data in D-Cache before disable D-Cache.
After disable D-Cache, the first store instructions in
psci_v7_flush_dcache_all will directly store registers
{r4-r5, r7, r9-r11, lr} to memory.
If there is dirty data before disable D-Cache,
psci_v7_flush_dcache_all will flush data to memory,
and may overwrite the memory that hold the registers
{r4-r5, r7, r9-r11, lr}.

So before disable cache, first flush D-Cache.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Hongbo Zhang <hongbo.zhang@nxp.com>
Cc: York Sun <york.sun@nxp.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Tom Rini <trini@konsulko.com>

arch/arm/cpu/armv7/psci.S

@@ -258,6 +258,10 @@ ENDPROC(psci_enable_smp)
 ENTRY(psci_cpu_off_common)
 	push	{lr}
 
+	bl	psci_v7_flush_dcache_all
+
+	clrex					@ Why???
+
 	mrc	p15, 0, r0, c1, c0, 0		@ SCTLR
 	bic	r0, r0, #(1 << 2)		@ Clear C bit
 	mcr	p15, 0, r0, c1, c0, 0		@ SCTLR