nvmem: Add bindings for simple nvmem framework

This patch adds bindings for simple nvmem framework which allows nvmem
consumers to talk to nvmem providers to get access to nvmem cell data.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[Maxime Ripard: intial version of eeprom framework]
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>