dt-bindings: clock: imx7ulp: remove SNVS clock

Since i.MX7ULP B0 chip, SNVS module is moved into M4
domain, so remove it from Linux clock table.

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