openrisc: Add _text symbol to fix ksym build error

The build robot reports:

.tmp_kallsyms1.o: In function `kallsyms_relative_base':

This is when using 'make alldefconfig'. Adding this _text symbol to mark the start of the kernel as in other architecture fixes this.

---
Change in v2:
- dont add _data since its not needed

 arch/openrisc/kernel/vmlinux.lds.S | 2 ++
 1 file changed, 2 insertions(+)

index ef31fc2..5525446 100644
@@ -44,6 +44,8 @@ SECTIONS
         /* Read-only sections, merged into text segment: */
         . = LOAD_BASE ;
 
+	_text = .;
+
 	/* _s_kernel_ro must be page aligned */
 	. = ALIGN(PAGE_SIZE);
 	_s_kernel_ro = .;

2.7.4