clk: imx7ulp: remove snvs clock

Since i.MX7ULP B0 chip, the SNVS module is moved into M4
domain and its clock is also moved into PCC0 which is
contorlled by M4, Linux kernel should NOT add it into
clock tree.

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