arm64: dts: zynqmp: Remove undocumented u-boot properties

u-boot, DT properties are not documented anywhere in Linux DT binding
that's why remove them.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/8ba339425b9c9f319bdedce7741367055a30713c.1598257720.git.michal.simek@xilinx.com
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>