alpha: simplify TIF_NEED_RESCHED handling

In case we have both NEED_RESCHED and SIGPENDING/NOTIFY_RESUME,
handle the latter first.  We'll get to original priorities in
the next commit, but now that allows to simplify the treatment
of NEED_RESCHED-only case nicely.  Namely, now there no need to
preserve the data for restarts across the call of schedule() in
$work_resched; we can get there only if we had either returned
from syscall without SIGPENDING (in which case we should've
had no restart-worthy return value and want no restarts) or
already got through do_notify_resume() call (in which case we
want no restarts anymore).  So we can just slap 0 into $19
instead of preserving it (and $20).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/alpha/kernel/entry.S

@@ -372,26 +372,18 @@ $ret_success:
 	.align	4
 	.ent	work_pending
 work_pending:
-	and	$5, _TIF_NEED_RESCHED, $2
-	beq	$2, $work_notifysig
+	and	$5, _TIF_NOTIFY_RESUME | _TIF_SIGPENDING, $2
+	bne	$2, $work_notifysig
 
 $work_resched:
-	subq	$sp, 16, $sp
-	stq	$19, 0($sp)              /* save syscall nr */
-	stq	$20, 8($sp)              /* and error indication (a3) */
+	/*
+	 * We can get here only if we returned from syscall without SIGPENDING
+	 * or got through work_notifysig already.  Either case means no syscall
+	 * restarts for us, so let $19 and $20 burn.
+	 */
 	jsr	$26, schedule
-	ldq	$19, 0($sp)
-	ldq	$20, 8($sp)
-	addq	$sp, 16, $sp
-	/* Make sure need_resched and sigpending don't change between
-		sampling and the rti.  */
-	lda	$16, 7
-	call_pal PAL_swpipl
-	ldl	$5, TI_FLAGS($8)
-	and	$5, _TIF_WORK_MASK, $2
-	beq	$2, restore_all
-	and	$5, _TIF_NEED_RESCHED, $2
-	bne	$2, $work_resched
+	mov	0, $19
+	br	ret_to_user
 
 $work_notifysig:
 	mov	$sp, $16