parisc/signal: Add FPE_CONDTRAP for conditional trap handling

Posix and common sense requires that SI_USER not be a signal specific
si_code. Thus add a new FPE_CONDTRAP si_code for conditional traps.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>