thermal: imx: Add nvmem-cells alternate binding for OCOTP access

On newer imx SOCs accessing OCOTP directly is wrong because the ocotp
clock needs to be enabled first. Add a binding for accessing the same
values through the imx-ocotp nvmem driver using nvmem-cells. This is
similar to other thermal drivers.

The old binding is preserved for compatibility and because it still
works fine on imx6qdl series chips.

In theory this problem could be solved by adding a reference to the
OCOTP clock instead but it is better to hide such details in a specific
nvmem driver.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>