dt-bindings: soc: imx: add i.MX8MP vpu blk ctrl

i.MX8MP VPU blk ctrl module has similar design as i.MX8MM, so reuse
the i.MX8MM VPU blk ctrl yaml file. And add description for the items.

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