openrisc: Fix conflicting types for _exext and _stext

The printk tree in linux-next has a patch "symbol lookup: introduce
dereference_symbol_descriptor()" that includes sections.h in kallsyms.h,
so arch/openrisc/kernel/traps.c gets a second extern definition for
_etext and _stext.

Remove the local definitions and include sections.h directly in
preparation for the kallsyms.h change.

This fixes the following (future) build error:

  CC      arch/openrisc/kernel/traps.o
arch/openrisc/kernel/traps.c:43:13: error: conflicting types for ‘_etext’
 extern char _etext, _stext;
             ^
In file included from ./arch/openrisc/include/generated/asm/sections.h:1:0,
                 from ./include/linux/kallsyms.h:15,
                 from arch/openrisc/kernel/traps.c:35:
./include/asm-generic/sections.h:35:32: note: previous declaration of ‘_etext’ was here
 extern char _text[], _stext[], _etext[];
                                ^

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>