parisc: Add HWPOISON page fault handler code

Commit 24587380 ("parisc: Add MADV_HWPOISON and MADV_SOFT_OFFLINE") added
the necessary constants to handle hardware-poisoning. Those were needed to
support the page deallocation feature from firmware.

But I completely missed to add the relevant fault handler code. This now
showed up when I ran the madvise07 testcase from the Linux Test Project,
which failed with a kernel BUG at arch/parisc/mm/fault.c:320.

With this patch the parisc kernel now behaves like other platforms and
gives the same kernel syslog warnings when poisoning pages.

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