ext: debug: segger: Fix SEGGER header inclusion

Fix issue caused by 3fc497ac9af7119e0e56d4b7fe2e47d6ae12cd8a

This change removes `rtt` and `systemview` from header includes
as these are already placed in the path.

Also `SEGGER_SYSVIEW_ConfDefaults.h` header included from
`SEGGER_SYSVIEW_Int.h` is placed higher to make sure `INLINE`
definition is properly visible.

Signed-off-by: Pawel Dunaj <pawel.dunaj@nordicsemi.no>