ARM: cpu: Add ARMv7 barrier operations support

This enables ARMv7 barrier operations support when
march=armv7-a is enabled.

Using CP15 barriers causes U-Boot bootm command crash when
transferring control to the loaded image on Renesas R8A7794 Cortex A7 CPU.
Using ARMv7 barrier operations instead of the deprecated CP15 barriers
helps to avoid these issues.

Signed-off-by: Valentine Barshak <valentine.barshak+renesas@cogentembedded.com>
Signed-off-by: Vladimir Barinov <vladimir.barinov+renesas@cogentembedded.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>