Kconfig: Provide name to orphan configuration choice symbol

Kconfig choice section for LINKER_ORPHAN configuration has no name.
This prevents configuring a default value in .defconfig files and
constrain to set in _defconfig /.prj files.
Then it is not possible to generalize this setting to a whole set of
boards (soc series for instance) or make it dependent on another symbol.
Provide it a name to add this flexibility.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>