dt-bindings: nvmem: add description for UniPhier eFuse

Add uniphier-efuse dt-bindings documentation.

Signed-off-by: Keiji Hayashibara <hayashibara.keiji@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>