board:samsung:common: move max77686 init function

This patch moves board specific max77686 init function from
common board to smdk5250 board file.

Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Rajeshwari S Shinde <rajeshwari.s@samsung.com>
Cc: Rajeshwari Birje <rajeshwari.birje@gmail.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>