parisc: Drop TIF_RESTORE_SIGMASK and switch to generic code

Commit 7e781418

 ("signal: consolidate {TS,TLF}_RESTORE_SIGMASK code")
introduced code with which the "restore sigmask" flag lives in task_struct
instead of ti->flags. Let's use this optimization on parisc too.

Signed-off-by: Helge Deller <deller@gmx.de>