ARM: dts: imx7ulp: add ocotp support

Add i.MX7ULP OCOTP support, its clock source is from
M4 BUS clock which is NOT available in Linux clock tree,
but M4 BUS clock is always ON when A7 (Linux) is alive,
so just use dummy clock here.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>