i2c: bma250: gyro wake: adding f2w_sensitivity_values attr

to mark possible values and current sensitivity (for tweak apps)
e.g.: [0] 1 or 0 [1], showing 0 and 1 as possible values and which is
selected (with brackets).

Change-Id: Ie074a513002306d0c1c0fb5f329306194680e3ef