platform/chrome: mfd/cros_ec_dev: Add sysfs entry to set keyboard wake lid angle

This adds a sysfs attribute (/sys/class/chromeos/cros_ec/kb_wake_angle)
used to set and get the keyboard wake lid angle. This attribute is
present only if 2 accelerometers are controlled by the EC.

This patch also moves the cros_ec features check before the device is
added so the features map obtained from the EC is ready on time.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Benson Leung <bleung@chromium.org>