mfd: ene-kb3930: Add driver for ENE KB3930 Embedded Controller

This driver provides access to the EC RAM of said embedded controller
attached to the I2C bus as well as optionally supporting its slightly weird
power-off/restart protocol.

A particular implementation of the EC firmware can be identified by a
model byte. If this driver identifies the Dell Ariel platform, it
registers the appropriate cells.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>

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Changes since v2:
- Sort the includes
- s/EC_MODEL_ID/EC_MODEL/
- Add a couple of clarifying comments
- Use #defines for values used in poweroff routine
- Remove priority from a restart notifier block
- s/priv/ddata/
- s/ec_ram/ram_regmap/ for the regmap name
- Fix the error handling when getting off gpios was not successful
- Remove a useless dev_info at the end of probe()
- Use i2c probe_new() callback, drop i2c_device_id
- Modify the logic in checking the model ID
3 files changed