This changes the hash insertion routines to return an error instead of
calling panic() when HV refuses to insert a HPTE (the hypervisor call to
set up a hashtable PTE is H_ENTER). 

The error is now propagated upstream, and either bad_page_fault() is
called (kernel mode) or a SIGBUS signal is forced (user mode).  Some
other panic() cases are also turned into BUG_ON.

Overall, this should provide us with better debugging data if the
problem happens, and avoids errors from userland mapping /dev/mem and
trying to use forbidden IOs (XFree ?) to bring the whole kernel down.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>