clk: mvebu: armada-37xx-periph: add PCIe gated clock

The PCIe clock is a gated clock which has the same source as GbE0
(both IPs share a set of registers). This source clock is called
'gbe_core' in the driver.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lkml.kernel.org/r/20190627125245.26788-2-miquel.raynal@bootlin.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>