display: state-transition: Relocate check_lcdoff_direct()

display: state-transition: Relocate check_lcdoff_direct()

check_lcdoff_direct() is used to check if display state can go to S_LCDOFF.
All plugins follows same policy of this function.

Thus, this function is added below display-state-transition.
- bool display_state_transition_is_possible_to_go_lcdoff(void);
    -> This replaces check_lcdoff_direct().

Also, new function is added below display-plugin.
- int display_plugin_config_get_dimming(int *dimming);
    -> It gets dimming config value from the conf file.
To confirm going to S_LCDOFF state, dimming value must also be checked.
So, display_plugin_config_get_dimming() is added too.

Change-Id: I19545fa1d6e7592a938a24e0b130302d88d81e02
Signed-off-by: Yunhee Seo <yuni.seo@samsung.com>