parisc: fix ptrace breakage

1) PTRACE_SYSCALL doesn't work for 64bit process on parisc64.
Compat syscall table is used instead of 64bit one.  IMO we should either
refuse to allow PTRACE_SYSCALL for 64bit processes or duplicate the
logics choosing the right syscall table into .Ltracesys.

	2) if you have let the tracee run with PTRACE_SYSCALL and
it had stopped, you can use PTRACE_POKEUSR to modify syscall number
(r20) and arguments 1--4 (r26--r23).  Modifications will have effect.
However, modifying arguments 5 and 6 (r22 and r21 resp.) works only
when process (32bit one) runs on 64bit host - on 32bit one it has no
effect.  AFAICS, the diff below should fix that one.
Signed-off-by: NAl Viro <viro@ZenIV.linux.org.uk>
Tested-by: NJohn David Anglin <dave.anglin@bell.net>
Signed-off-by: NHelge Deller <deller@gmx.de>

arch/parisc/kernel/syscall.S

@@ -309,10 +309,13 @@ tracesys_next:
 	LDREG   TASK_PT_GR25(%r1), %r25
 	LDREG   TASK_PT_GR24(%r1), %r24
 	LDREG   TASK_PT_GR23(%r1), %r23
-#ifdef CONFIG_64BIT
 	LDREG   TASK_PT_GR22(%r1), %r22
 	LDREG   TASK_PT_GR21(%r1), %r21
+#ifdef CONFIG_64BIT
 	ldo	-16(%r30),%r29			/* Reference param save area */
+#else
+	stw     %r22, -52(%r30)                 /* 5th argument */
+	stw     %r21, -56(%r30)                 /* 6th argument */
 #endif
 
 	comiclr,>>=	__NR_Linux_syscalls, %r20, %r0