s390/linker skript: discard exit.data at runtime

Discard exit.data section at run time, not link time, since exit.text
references exit.data and causes this build error:

`.exit.data' referenced in section `.exit.text' of drivers/built-in.o:
 defined in discarded section `.exit.data' of drivers/built-in.o
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/vmlinux.lds.S

@@ -75,6 +75,10 @@ SECTIONS
 		EXIT_TEXT
 	}
 
+	.exit.data : {
+		EXIT_DATA
+	}
+
 	/* early.c uses stsi, which requires page aligned data. */
 	. = ALIGN(PAGE_SIZE);
 	INIT_DATA_SECTION(0x100)