dt-bindings: nvmem: Add Spreadtrum eFuse controller documentation

This patch adds the binding documentation for Spreadtrum eFuse controller.

Signed-off-by: Freeman Liu <freeman.liu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>