ARM: dts: socfgpa: set bridges status to disabled

The hps-to-fpga bridges can't be used, when the FPGA is not programmed.
Set the default state to disabled and leave enabling them to the board-specific
dts files.
Although this changes behavior, there are no in-tree users of the bridges, so
this won't break anything.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>