arm64: dts imx8mn: Remove non-existent USB OTG2

According to the i.MX8MN TRM, there is only one OTG port.  The
address for OTG2 is reserved on Nano.

This patch removes the non-existent OTG2, usbphynop2, and the usbmisc2
nodes.

Fixes: 6c3debcb ("arm64: dts: freescale: Add i.MX8MN dtsi support")
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>