MAINTAINERS: powerpc: Add Aneesh & Naveen

Aneesh and Naveen are helping out with some aspects of upstream
maintenance, add them as reviewers.

Acked-by: "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org>
Acked-by: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231205051105.736470-1-mpe@ellerman.id.au