clk: mvebu: create parent-child relation for PCIe clocks on Armada 370

The Armada 370 has two gatable clocks for each PCIe interface, and we
want both of them to be enabled. We therefore make one of the two
clocks a child of the other, as we did for the sataX and sataXlnk
clocks on Armada XP.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>