s390: move __amode31_base declaration to proper header file

Move __amode31_base declaration to proper header file to get rid of

arch/s390/boot/startup.c:24:15:
 warning: symbol '__amode31_base' was not declared. Should it be static?
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/setup.h

@@ -76,6 +76,7 @@ extern unsigned long ident_map_size;
 extern unsigned long pgalloc_pos;
 extern unsigned long pgalloc_end;
 extern unsigned long pgalloc_low;
+extern unsigned long __amode31_base;
 
 /* The Write Back bit position in the physaddr is given by the SLPC PCI */
 extern unsigned long mio_wb_bit_mask;

arch/s390/kernel/entry.h

@@ -73,6 +73,5 @@ extern struct exception_table_entry _stop_amode31_ex_table[];
 #define __amode31_data __section(".amode31.data")
 #define __amode31_ref __section(".amode31.refs")
 extern long _start_amode31_refs[], _end_amode31_refs[];
-extern unsigned long __amode31_base;
 
 #endif /* _ENTRY_H */