clk: berlin: prepare simple-mfd conversion

Prepare conversion of berlin clk drivers to a simple-mfd sub-node by
checking for parent node compatible. If parent node is "syscon" compatible
use it for of_iomap instead of the own node.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>