dt-bindings: nvmem: Add Spreadtrum SC27XX efuse controller documentation

This patch adds the binding documentation for Spreadtrum SC27XX series
PMICs efuse controller device.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>