powerpc/pseries: Quieten relocation on exceptions warning

The H_SET_MODE hcall returns H_P2 if a function is not implemented
and all callers should handle this case.

The call to enable relocation on exceptions currently prints an error
message if the feature is not implemented. While H_SET_MODE was
first introduced on POWER8 (which has relocation on exceptions), it
has been now added on some POWER7 configurations (which does not).

Check for H_P2 and print an informational message instead.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>