platform/chrome: cros_ec: add common commands for EC codec

Add the following common commands:
- GET_CAPABILITIES
- GET_SHM_ADDR
- SET_SHM_ADDR

Acked-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20191017213539.04.Idc3c6e1cd94b70bf010249928d4a93c6c90495b7@changeid


Signed-off-by: Mark Brown <broonie@kernel.org>