display: Relocate device-interface.h to core

display: Relocate device-interface.h to core

Delete the code that was unnecessary in "core.h" file.
"core.h" includes "device-interface.h" file.
However, that is not necessary for "core.h".
Also it can cause build warning in terms of including relationships.
Thus, "device-interface.h" is included to other files which were including "core.h"
to remove build dependency.

Change-Id: I3828be74d41a11445d518b2a65e19ab66eb3e6f6
Signed-off-by: Yunhee Seo <yuni.seo@samsung.com>