dt-bindings: clock: add i.MX8M Anatop

i.MX8M Family features an anatop module the produces PLL to clock
control module(CCM) root clock. Add the missing yaml file.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>