display: state-transition: Relocate update_lcdoff_source()

display: state-transition: Relocate update_lcdoff_source()

update_lcdoff_source() is used for setting lcdoff reason.
This function is called when the display state goes to lcdoff state.
Same code was copied and used in all plugins.

Thus, this function is added below display-state-transition
int display_state_transition_update_lcdoff_reason(int source);
-> This function sets the lcdoff reason to VCONFKEY_PM_LCDOFF_SOURCE.

Change-Id: Idc857d4b52502612eaccb01373d984815806a153
Signed-off-by: Yunhee Seo <yuni.seo@samsung.com>