ARM: berlin: add SMP support

Adds SMP support for Berlin SoCs. Secondary CPUs are reset, then
execute the instruction we put in the reset exception register, setting
the pc at the address contained in the software reset address register,
which is the physical address of the Berlin secondary startup.

This implementation avoid using the pen lock mechanism.

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>