s390: Correct register corruption in critical section cleanup

In the critical section cleanup we must not mess with r1.  For march=z9
or older, larl + ex (instead of exrl) are used with r1 as a temporary
register. This can clobber r1 in several interrupt handlers. Fix this by
using r11 as a temp register.  r11 is being saved by all callers of
cleanup_critical.

Fixes: 6dd85fbb ("s390: move expoline assembler macros to a header")
Cc: stable@vger.kernel.org #v4.16
Reported-by: NOliver Kurz <okurz@suse.com>
Reported-by: NPetr Tesařík <ptesarik@suse.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NHendrik Brueckner <brueckner@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -1265,7 +1265,7 @@ cleanup_critical:
 	jl	0f
 	clg	%r9,BASED(.Lcleanup_table+104)	# .Lload_fpu_regs_end
 	jl	.Lcleanup_load_fpu_regs
-0:	BR_EX	%r14
+0:	BR_EX	%r14,%r11
 
 	.align	8
 .Lcleanup_table:
@@ -1301,7 +1301,7 @@ cleanup_critical:
 	ni	__SIE_PROG0C+3(%r9),0xfe	# no longer in SIE
 	lctlg	%c1,%c1,__LC_USER_ASCE		# load primary asce
 	larl	%r9,sie_exit			# skip forward to sie_exit
-	BR_EX	%r14
+	BR_EX	%r14,%r11
 #endif
 
 .Lcleanup_system_call: