parisc: Drop per_cpu uaccess related exception_data struct

The last users have been migrated off by commits d19f5e41 ("parisc:
Clean up fixup routines for get_user()/put_user()") and 554bfece
("parisc: Fix access fault handling in pa_memcpy()").

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