MAINTAINERS: add myself as maintainer for xilinx axiethernet driver

I am maintaining xilinx axiethernet driver in xilinx tree and would like
to maintain it in the mainline kernel as well. Hence adding myself as a
maintainer. Also Anirudha and John has moved to new roles, so based on
request removing them from the maintainer list.

Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Acked-by: John Linn <john.linn@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>