parisc: Fix lpa and lpa_user defines

While working on the rewrite to the light-weight syscall and futex code, I
experimented with using a hash index based on the user physical address of
atomic variable. This exposed two problems with the lpa and lpa_user defines.

Because of the copy instruction, the pa argument needs to be an early clobber
argument. This prevents gcc from allocating the va and pa arguments to the same
register.

Secondly, the lpa instruction can cause a page fault so we need to catch
exceptions.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Fixes: 116d7533 ("parisc: Use lpa instruction to load physical addresses in driver code")
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.2+