Make get_lcd_power() use dpms to get lcd power

Make get_lcd_power() use dpms to get lcd power

Deviced used to set lcd power by requesting to dpms(dpms_set_state), but
get lcd power by reading node directly through HAL(display_dev->get_state).
To make this get/set machanism same, get mechanism changed to use
dpms(dpms_get_state), removed all regarding HAL. Also, make dpms_get_state
synchronous and dpms_set_state asynchronous to ensure latency issue.

Change-Id: Ib93cb55d18f3e175a16c7138288b09ac76d25f05
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>