[S390] kernel: Initialize register 14 when starting new CPU

When starting a new CPU we currently jump to start_secondary() without
setting register 14 (the return address) correctly. Therefore on the stack
frame for start_secondary an invalid return address is stored. This leads
to wrong stack back traces in kernel dumps.

Example:

 #00 [1f33fe48] cpu_idle at 10614a
 #01 [1f33fe90] start_secondary at 54fa88
 #02 [1f33feb8] (null) at 0                 <--- invalid

To fix this start_secondary() is called now with basr/brasl that sets
register 14 correctly. The output of the stack backtrace looks then
like the following:

 #00 [1f33fe48] cpu_idle at 10614a
 #01 [1f33fe90] start_secondary at 54fa88
 #02 [1f33feb8] restart_base at 54f41e      <--- correct
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -836,7 +836,7 @@ restart_base:
 	stosm	__SF_EMPTY(%r15),0x04	# now we can turn dat on
 	basr	%r14,0
 	l	%r14,restart_addr-.(%r14)
-	br	%r14			# branch to start_secondary
+	basr	%r14,%r14		# branch to start_secondary
 restart_addr:
 	.long	start_secondary
 	.align	8

arch/s390/kernel/entry64.S

@@ -841,7 +841,7 @@ restart_base:
 	mvc	__LC_SYSTEM_TIMER(8),__TI_system_timer(%r1)
 	xc	__LC_STEAL_TIMER(8),__LC_STEAL_TIMER
 	stosm	__SF_EMPTY(%r15),0x04	# now we can turn dat on
-	jg	start_secondary
+	brasl	%r14,start_secondary
 	.align	8
 restart_vtime:
 	.long	0x7fffffff,0xffffffff