arm64: zynqmp: Do not expose usbhub nodes

Upstream dwc3 U-Boot driver is not able to handle child nodes properly
that's why comment them in DT for now. This patch should be reverted when
dwc3 driver handles it properly.
DT node itself is aligned with dt schema.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/537c91a7ac0843358c4e33aa10d9e035d8e92faf.1699286139.git.michal.simek@amd.com