powerpc/powernv: only call OPAL_ELOG_RESEND if firmware supports it

Otherwise firmware complains: "OPAL: Called with bad token 74 !"
as not all OPAL systems have the ability to resend error logs.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Acked-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>