powerpc/numa: convert printk to pr_xxx

Convert the remaining printk to pr_xxx
One advantage would be all prints will now have prefix "numa:" from
pr_fmt().

[ convert printk(KERN_ERR) to pr_warn : Suggested by Laurent Dufour ]
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
[mpe: Rebase onto powerpc/next, s/WARNING/Warning/]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210826100521.412639-3-srikar@linux.vnet.ibm.com