spapr: Generate random HASHPKEYR for spapr machines

spapr: Generate random HASHPKEYR for spapr machines

The hypervisor is expected to create a value for the HASHPKEY SPR for
each partition. Currently it uses zero for all partitions, use a
random number instead, which in theory might make kernel ROP protection
more secure.

Signed-of-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241219034035.1826173-4-npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>