nvmem: add a driver for the Amlogic Meson6/Meson8/Meson8b SoCs

This adds a driver to access the efuse on Amlogic Meson6, Meson8 and
Meson8b SoCs.
These SoCs are accessing the efuse IP block directly through the
registers in the "secbus" region. This makes it different from the Meson
GX efuse driver which uses the "secure monitor" firmware to access the
efuse.

The efuse on Meson6 can only read one byte at a time, while the efuse on
Meson8 and Meson8b always reads 4 bytes at a time. The new driver
supports both, but due to lack of hardware Meson6 support was not tested.

The hardware also supports writing. However, this is currently not
supported by the driver.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>