power: pmic: remove pmic_max8997/8 files

Remove pmic_max8997/8 files about no-DM.
There are already existed max8997/8 as driver-model.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>