display: Move functions related to display status(on/off/dim/standby)

display: Move functions related to display status(on/off/dim/standby)
	from plugin to core display module

Remove and redefine display status change functions.
These functions are added below display-panel/display-backlight.

int display_panel_set_panel_state_by_on_state(enum device_flags flags)
int display_panel_set_panel_state_by_off_state(enum device_flags flags)
int display_panel_set_panel_state_by_standby_state(bool standby_on)
int display_backlight_set_brightness_by_dim_brightness(void)
-> With these functions, it is possible to change display panel/backlight status.

Change-Id: I4313046c610410ccef82ac18fda1e334960330b1
Signed-off-by: Yunhee Seo <yuni.seo@samsung.com>